Author name code: kowalski
ADS astronomy entries on 2022-09-14
author:"Kowalski, Adam"
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Title: Development of Integral Field Spectrographs to Revolutionize
Spectroscopic Observations of Solar Flares and other Energetic
Solar Eruptions
Authors: Lin, Haosheng; Anan, Tetsu; Cauzzi, Gianna; Fletcher, Lyndsay;
Huang, Pei; Kowalski, Adam; Kramar, Maxim; Qiu, Jiong; Samra, Jenna;
Spittler, Constance; Sukegawa, Takashi; Wirth, Gregory
Bibcode: 2022arXiv220900788L
Altcode:
The Sun's proximity offers us a unique opportunity to study in detail
the physical processes on a star's surface; however, the highly dynamic
nature of the stellar surface -- in particular, energetic eruptions
such as flares and coronal mass ejections -- presents tremendous
observational challenges. Spectroscopy probes the physical state of
the solar atmosphere, but conventional scanning spectrographs and
spectrometers are unable to capture the full evolutionary history of
these dynamic events with a sufficiently wide field of view and high
spatial, spectral, and temporal resolution. Resolving the physics of the
dynamic sun requires gathering simultaneous spectra across a contiguous
area over the full duration of these events, a goal now tantalizingly
close to achievable with continued investment in developing powerful
new Integral Field Spectrographs to serve as the foundation of both
future ground- and space-based missions. This technology promises to
revolutionize our ability to study solar flares and CMEs, addressing
NASA's strategic objective to "understand the Sun, solar system, and
universe." Since such events generate electromagnetic radiation and
high-energy particles that disrupt terrestrial electric infrastructure,
this investment not only advances humanity's scientific endeavors
but also enhances our space weather forecasting capability to protect
against threats to our technology-reliant civilization.
Title: Photospheric Spectral Line Velocity Diagnostics in Solar and
Stellar Flares.
Authors: Monson, Aaron; Milligan, Ryan; Kowalski, Adam; Mathioudakis,
Mihalis
Bibcode: 2022cosp...44.2449M
Altcode:
We present radiative-hydrodynamic simulations of solar flares generated
by the RADYN and RH codes to study the perturbations induced in
photospheric Fe I lines by electron beam heating. We investigate the
induced line-of-sight velocities by various electron beam parameter
combinations, and the primary energy transport mechanisms responsible
for heating the lower solar atmosphere. From these models, we synthesize
several deep forming Fe I spectral lines and study the Doppler velocity
information retrievable during the flare. It is shown that throughout
the period of beam heating a significant proportion of the line
intensity is contributed from the chromosphere, leading to erroneous
Doppler shifts not reflective in the photospheric LOS velocities. The
apparent m/s Doppler shifts can even indicate false downflows in the
photosphere, making their study vital for correctly considering momentum
transfer throughout the lower solar atmosphere. We have expanded our
analysis to stellar flare scenarios, where the sensitivity of these deep
forming spectral lines provides a powerful diagnostic tool for analysing
extreme stellar flare effects and features in the chromosphere.
Title: Coronal Dimming as a Proxy for Solar and Stellar Coronal
Mass Ejections
Authors: Jin, Meng; Nitta, Nariaki; Derosa, Marc; Cheung, Mark; Osten,
Rachel; France, Kevin; Mason, James; Kowalski, Adam; Schrijver, Carolus
Bibcode: 2022cosp...44.1404J
Altcode:
Solar coronal dimmings have been observed extensively in the past two
decades. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings as well as their relationship
with CMEs. Recent study (e.g., Veronig et al. 2021) also shows promising
dimming signals from distant stars, which suggest the possibility of
using coronal dimming as a proxy to diagnose stellar CMEs. In this
study, we first conduct a comparative study of solar coronal dimming
using MHD simulations and SDO observations. A detailed analysis of
the simulation and observation data reveals how transient dimming
/ brightening are related to plasma heating processes, while the
long-lasting core and remote dimmings are caused by mass loss process
induced by the CME. Using metrics such as dimming depth and dimming
slope, we uncover a relationship between dimmings and CME properties
(e.g., CME mass, CME speed) in the simulation. We further extend the
model for simulating the stellar CMEs and dimmings and compare with
solar cases. Our result suggests that coronal dimmings encode important
information about the associated CMEs, which provides a physical basis
for detecting stellar CMEs from distant solar-like stars.
Title: Blue asymmetries in Balmer lines and possible mass ejections
during mid M dwarf flares
Authors: Notsu, Yuta; Shibata, Kazunari; Enoto, Teruaki; Hamaguchi,
Kenji; Honda, Satoshi; Maehara, Hiroyuki; Nogami, Daisaku; Ikuta,
Kai; Kowalski, Adam; Hawley, Suzanne; Davenport, James; Tristan,
Isaiah; Namekata, Kosuke
Bibcode: 2022cosp...44.1382N
Altcode:
Flares are releases of magnetic energy in the solar/stellar atmosphere,
and they have strong emissions from radio to X-rays. During some M
dwarf flares, chromospheric line profiles show blue asymmetries (Honda
et al. 2018), although red asymmetries are more commonly observed in
solar flares. Similar enhancements of the blue wings of Balmer lines
may provide clues for investigating the early phases of stellar coronal
mass ejections (CMEs) during flares (cf. Vida et al. 2016&2019), but
this is still controversial. Thus, we need simultaneous spectroscopic
and photometric observations of flares with high time resolution
to understand the relationship between mass ejections and flaring
events. We have conducted simultaneous spectroscopic and photometric
observations of mid M dwarf flare stars (YZCMi, EVLac, ADLeo) using
APO 3.5m/ARCES, SMARTS 1.5m/CHIRON, Nayuta 2m/MALLS (high-dispersion
spectroscopy), TESS (space high-precision single-color photometry),
ground-based 0.4-1m telescopes (ground-based photometry), and NICER
(X-ray spectroscopy). During 34 nights of observations, we detected more
than 46 flares in Balmer lines (e.g. H$\alpha$). Among them, at least
8 flare event showed clear blue asymmetries with velocities 100-200
km s$ ^{-1}$(Maehara et al. 2021 PASJ, Notsu et al. in prep). We
found various correspondences in the durations of blue asymmetries
and intensities of white light emissions. In most cases, while the
blue asymmetries were not significant in the higher-order Balmer lines
and other chromospheric lines such as the Ca II K/8542A line. As for
one event, we succeeded in the simultaneous observation of the blue
asymmetry and X-ray flare for the first time. These results might
be a clue to investigate the formation processes of the blue-shifted
components, and discuss how blue asymmteries are helpful for dicussing
CME properties. By assuming that the blue asymmetries were caused by
prominence eruptions, we estimate the mass and kinetic energy of the
upward-moving material to be 10$ ^{15}$ — 10$ ^{18}$ g and 10$ ^{29}$
—10$ ^{32}$ erg, respectively. The estimated masses are comparable
to expectations from the empirical relation between the flare X-ray
energy and mass of upward-moving material for stellar flares and
solar CMEs. In contrast, the estimated kinetic energies for these
non-white-light flares are roughly 2-3 orders of magnitude smaller than
that expected from the relation between flare X-ray energy and kinetic
energy for solar CMEs. This could be understood by the difference in
the velocity between CMEs and prominence eruptions.
Title: Simultaneous Multi-wavelength Study of Flares on nearby active
star Wolf 359
Authors: Paudel, Rishi; Barclay, Thomas; Schlieder, Joshua; Quintana,
Elisa; Youngblood, Allison; Gilbert, Emily; Vega, Laura; Osten,
Rachel; Hamaguchi, Kenji; Monsue, Teresa; Notsu, Yuta; Kowalski,
Adam; Tristan, Isaiah
Bibcode: 2022BAAS...54e.396P
Altcode:
During a flare, energy is released by a star at wavelengths spanning all
the way from X-rays to radio. By studying flares with multi-wavelength
datasets we can understand the correlation between energies and
different flare properties in various wavelengths. We obtained data
of nearby active star Wolf 359 using seven different observatories. We
obtained TESS optical data simultaneous with XMM-Newton X-ray, Swift UV
and X-ray, NICER X-ray and Australia Telescope Compact Array (ATCA)
radio, Las Cumbres Observatory Global Telescope (LCO-GT) near-UV
and Apache Point Observatory (APO) optical data on Wolf 359. This
provides an unprecedented number of overlapping measurements/wavelength
coverage. Such data will be used to study the flare energy partition
in X-ray/UV/optical/radio wavelength, and to study the full atmospheric
response to flares, including the action of accelerated particles. Our
results will be helpful in understanding the space-weather of stars
with spectral type and age comparable to Wolf 359.
Title: The Atmospheric Response to High Nonthermal Electron-beam
Fluxes in Solar Flares. II. Hydrogen-broadening Predictions for
Solar Flare Observations with the Daniel K. Inouye Solar Telescope
Authors: Kowalski, Adam F.; Allred, Joel C.; Carlsson, Mats; Kerr,
Graham S.; Tremblay, Pier-Emmanuel; Namekata, Kosuke; Kuridze, David;
Uitenbroek, Han
Bibcode: 2022ApJ...928..190K
Altcode: 2022arXiv220113349K
Redshifted components of chromospheric emission lines in the hard X-ray
impulsive phase of solar flares have recently been studied through
their 30 s evolution with the high resolution of the Interface Region
Imaging Spectrograph. Radiative-hydrodynamic flare models show that
these redshifts are generally reproduced by electron-beam-generated
chromospheric condensations. The models produce large ambient electron
densities, and the pressure broadening of the hydrogen Balmer series
should be readily detected in observations. To accurately interpret
the upcoming spectral data of flares with the DKIST, we incorporate
nonideal, nonadiabatic line-broadening profiles of hydrogen into the
RADYN code. These improvements allow time-dependent predictions for
the extreme Balmer line wing enhancements in solar flares. We study two
chromospheric condensation models, which cover a range of electron-beam
fluxes (1 - 5 × 1011 erg s-1 cm-2) and
ambient electron densities (1 - 60 × 1013 cm-3)
in the flare chromosphere. Both models produce broadening and
redshift variations within 10 s of the onset of beam heating. In the
chromospheric condensations, there is enhanced spectral broadening due
to large optical depths at Hα, Hβ, and Hγ, while the much lower
optical depth of the Balmer series H12-H16 provides a translucent
window into the smaller electron densities in the beam-heated layers
below the condensation. The wavelength ranges of typical DKIST/ViSP
spectra of solar flares will be sufficient to test the predictions
of extreme hydrogen wing broadening and accurately constrain large
densities in chromospheric condensations.
Title: High-resolution Near-infrared Spectroscopy of a Flare around
the Ultracool Dwarf vB 10
Authors: Kanodia, Shubham; Ramsey, Lawrence W.; Maney, Marissa;
Mahadevan, Suvrath; Cañas, Caleb I.; Ninan, Joe P.; Monson, Andrew;
Kowalski, Adam F.; Goumas, Maximos C.; Stefansson, Gudmundur;
Bender, Chad F.; Cochran, William D.; Diddams, Scott A.; Fredrick,
Connor; Halverson, Samuel; Hearty, Fred; Janowiecki, Steven; Metcalf,
Andrew J.; Odewahn, Stephen C.; Robertson, Paul; Roy, Arpita; Schwab,
Christian; Terrien, Ryan C.
Bibcode: 2022ApJ...925..155K
Altcode: 2021arXiv211114647K
We present high-resolution observations of a flaring event in the
M8 dwarf vB 10 using the near-infrared Habitable-zone Planet Finder
(HPF) spectrograph on the Hobby-Eberly Telescope. The high stability of
HPF enables us to accurately subtract a vB 10 quiescent spectrum from
the flare spectrum to isolate the flare contributions and study the
changes in the relative energy of the Ca II infrared triplet, several
Paschen lines, the He λ10830 triplet lines, and to select iron and
magnesium lines in HPF's bandpass. Our analysis reveals the presence
of a red asymmetry in the He λ10830 triplet, which is similar to
signatures of coronal rain in the Sun. Photometry of the flare derived
from an acquisition camera before spectroscopic observations and the
ability to extract spectra from up-the-ramp observations with the HPF
infrared detector enable us to perform time-series analysis of part of
the flare and provide coarse constraints on the energy and frequency
of such flares. We compare this flare with historical observations of
flares around vB 10 and other ultracool M dwarfs and attempt to place
limits on flare-induced atmospheric mass loss for hypothetical planets
around vB 10.
Title: Extreme-ultraviolet Stellar Characterization for Atmospheric
Physics and Evolution mission: motivation and overview
Authors: France, Kevin; Fleming, Brian; Youngblood, Allison; Mason,
James; Drake, Jeremy J.; Amerstorfer, Ute V.; Barstow, Martin;
Bourrier, Vincent; Champey, Patrick; Fossati, Luca; Froning, Cynthia
S.; Green, James C.; Grisé, Fabien; Gronoff, Guillaume; Hellickson,
Timothy; Jin, Meng; Koskinen, Tommi T.; Kowalski, Adam F.; Kruczek,
Nicholas; Linsky, Jeffrey L.; Lipscy, Sarah J.; McEntaffer, Randall
L.; McKenzie, David E.; Miles, Drew M.; Patton, Tom; Savage, Sabrina;
Siegmund, Oswald; Spittler, Constance; Unruh, Bryce W.; Volz, Máire
Bibcode: 2022JATIS...8a4006F
Altcode: 2022arXiv220113219F
The Extreme-ultraviolet Stellar Characterization for Atmospheric
Physics and Evolution (ESCAPE) mission is an astrophysics Small
Explorer employing ultraviolet spectroscopy (EUV: 80 to 825 Å and FUV:
1280 to 1650 Å) to explore the high-energy radiation environment
in the habitable zones around nearby stars. ESCAPE provides the
first comprehensive study of the stellar EUV and coronal mass
ejection environments that directly impact the habitability of rocky
exoplanets. In a 20-month science mission, ESCAPE will provide the
essential stellar characterization to identify exoplanetary systems
most conducive to habitability and provide a roadmap for NASA's
future life-finder missions. ESCAPE accomplishes this goal with
roughly two-order-of-magnitude gains in EUV efficiency over previous
missions. ESCAPE employs a grazing incidence telescope that feeds an
EUV and FUV spectrograph. The ESCAPE science instrument builds on
previous ultraviolet and x-ray instrumentation, grazing incidence
optical systems, and photon-counting ultraviolet detectors used on
NASA astrophysics, heliophysics, and planetary science missions. The
ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace
BCP-Small spacecraft. Data archives will be housed at the Mikulski
Archive for Space Telescopes.
Title: Spectral Runway: An Analysis of Solar Balmer Lines through
both Observations and Models
Authors: Burnham, Emilie; Criscuoli, Serena; Kowalski, Adam; Harder,
Jerald; Meisner, Randy
Bibcode: 2021AGUFMSH45B2367B
Altcode:
Spectral analysis provides a glimpse into the physical properties of
stellar atmospheres, which includes temperature, density, magnetic
signatures, and so on. Balmer lines specifically are used as proxies
for atmospheric activity, as they have been used to determine stellar
effective temperatures, and used to constrain stellar atmospheric
models. Here, we are interested in the variations of Balmer lines
induced by stellar surface magnetism, which is known to affect the
atmospheres of orbiting planets and is a factor in determining
their habitability. As direct solar measurements and spatially
resolved stellar spectra are not always available, models are vital
to the understanding of the magnetic contribution to stellar spectral
variability. In this context, the Sun offers a unique opportunity for
direct observations of the effects of magnetic features on spectral
irradiance and further validation with state-of-the-art models. In this
study we utilize high spatial resolution spectroscopic observations
obtained at the Dunn Solar Telescope to investigate how surface
magnetism affects the shape of Balmer line profiles, specifically
H-alpha and H-gamma. Observational results are then compared with
theoretical spectra obtained with the Rybiki and Hummer synthesis
code using two sets of one-dimensional solar atmospheric models (each
describing different types of quiet and active regions) published
in Fontenla et al. 1999 and Fontenla et al. 2011, respectively. At
this point, it seems that the 2011 models are an overall better
representation of our quiet sun observations than the 1999 models, for
the 1999 models have far deeper line profiles than would be expected for
the quiet sun atmospheric structures that were observed. By determining
the atmospheric models that best fit the observations, our results
provide important information for improving the understanding of the
solar atmosphere and for the modeling of stellar spectral variability
that would, in turn, impact the search for habitable exoplanets.
Title: Revisting the Orrall-Zirker Effect: Identifying the
suprathermal proton distribution during solar flares from Lyman
line emission
Authors: Kerr, Graham; Allred, Joel; Milligan, Ryan; Kowalski, Adam;
Hudson, Hugh
Bibcode: 2021AGUFMSH23B..04K
Altcode:
It is likely that ions are accelerated during solar flares. However,
due in large part to a lack of observational constraints on the
suprathermal ion population in flares, they are not usually considered
in energy transport models, with the focus being on flare accelerated
electrons. Gamma-ray observations are required to constrain the high
energy (MeV) protons, but lower energy (deka-keV to 1 MeV) protons
can potentially be detected through the Orrall-Zirker effect (Orrall
& Zirker, 1976). Suprathermal protons undergo charge exchange
with ambient neutral hydrogen, creating a population of suprathermal
neutral hydrogen. These energetic neutrals can subsequently emit
extremely Doppler shifted photons. The appearance of a very broad
redshifted feature in the far red wings of certain spectral lines
can indicate the presence of suprathermal ions, and the properties of
the feature has diagnostic potential of the distribution of those ions
(e.g. Brosius & Woodgate 1999). This effect is revisited here using
modern state-of-the-art flare simulations that track the ionisation
stratification and suprathermal proton distribution as a function of
time in proton beam driven flares (RADYN+FP, Allred et al 2020), and
using up-to-date charge exchange cross sections. We have developed a
post-processing radiation transfer code (OrrallZirkerPy) that takes
those flare atmospheres as input and makes time-dependent predictions
of red-shifted features. The characteristics of non-thermal emission
of Lyman alpha and Lyman beta, and their potential as diagnostics of
flare accelerated protons, are presented. These predictions are of
particular interest now that we have current and planned missions that
can observe these lines during solar flares (e.g. SolO/SPICE, SDO/EVE,
EUVST, SNIFS).
Title: Recent observations of stellar flares on G-, K-, and M-dwarf
stars and possible mass ejections
Authors: Notsu, Yuta; Kowalski, Adam; Maehara, Hiroyuki; Namekata,
Kosuke; Tristan, Isaiah; Okamoto, Soshi; Ikuta, Kai; Hawley, Suzanne;
Davenport, James; Enoto, Teruaki; Hamaguchi, Kenji; Nogami, Daisaku;
Shibata, Kazunari
Bibcode: 2021AGUFM.U43B..01N
Altcode:
Flares are frequent energetic explosions in the stellar atmosphere,
and are thought to occur by impulsive releases of magnetic energy
stored around starspots. Large flares (so called superflares) generate
strong high energy emissions and coronal mass ejections (CMEs), which
can greatly affect the planetary environment and habitability. Recent
Kepler/TESS photometric data have revealed the statistical properties
of superflares on G, K, M-type stars. Superflare stars are well
characterized by the existence of large starspots on the surface,
and their magnetic fluxes can explain well superflare energies. Flare
frequency/energy depends on stellar rotation period and stellar
temperature. Young rapidly-rotating stars and cooler stars tend to
have frequent flares, which can be more hazardous for the habitable
planets. However, we still do not know the emission mechanisms of
superflares, and how large CMEs are associated with superflares on these
active stars. Then recently, these active superflare stars have been
investigated in more detail thorugh recent multi-wavelength surveys. For
example, Hydrogen chromospheric lines during flares show blue-shifted
profiles, which can give us some hints on dynamics or mass ejections
during superflares. In the early part of this invited overview talk,
I briefly overview the recent statistical results of superflares from
Kepler/TESS data. Then in the latter part, I also briefly discuss the
results of recent multi-wavelength campaign observations of superflares,
and discuss possible detections of mass ejections (stellar CMEs).
Title: Statistical Analysis of Impulsiveness and Rise Phase Duration
of Solar Flares in the He II 304 Angstrom Chromospheric Line
Authors: Tamburri, Cole; Kazachenko, Maria; Kowalski, Adam
Bibcode: 2021AGUFMSH25E2126T
Altcode:
We perform statistical analysis of solar flare light curves and ribbon
morphology to advance our understanding of flare impulsiveness, an
important parameter to describe stellar flares. The Solar Dynamics
Observatory Extreme Ultraviolet Variability Experiment (SDO/EVE)
provides "Sun-as-a-star" data corresponding to the variability of
the Suns irradiance in the XUV and EUV wavelengths (from 0.1 to 106
nm). Using EVE light curves in the 304 Angstrom line, we study 2049
solar flares from 30 April 2010 to 26 May 2014. We present an algorithm
for fitting the flare light curves in the 304 Angstrom line, emitted by
He II at around 50000 K from the chromosphere and transition region
and therefore representative of the dominant source of radiation
in a solar flare. We use this algorithm to identify particularly
high signal-to-noise flare light curves within the database, with
representatives from C, M, and X flare classes. The parameters
of the model associated with each flare can be used to identify
notable features such as the incidence of multiple peaks in the rise
phase. Identification of the rise and decay phases for each flare allows
us to compare rise phase duration and flare impulsiveness to geometrical
and physics-based properties of each flare, an important step in
advancing our understanding of flare energy release. Specifically,
using SDO Atmospheric Imaging Assembly (SDO/AIA) instrument data in
the 1600 Angstrom line, we analyze the flare morphology and energy
release in the context of the "impulsiveness" classification scheme for
a sub-sample of the flares. We also compare this index to several solar
flare properties including duration, peak X-ray flux, reconnection rate,
and quasi-periodic pulsation (QPP) period, among others.
Title: VizieR Online Data Catalog: IRD and HPF spectra of
TRAPPIST-1b,e and f (Krishnamurthy+, 2021)
Authors: Krishnamurthy, V.; Hirano, T.; Stefansson, G.; Ninan, J. P.;
Mahadevan, S.; Gaidos, E.; Kopparapu, R.; Sato, B.; Hori, Y.; Bender,
C. F.; Canas, C. I.; Diddams, S. A.; Halverson, S.; Harakawa, H.;
Hawley, S.; Hearty, F.; Hebb, L.; Hodapp, K.; Jacobson, S.; Kanodia,
S.; Konishi, M.; Kotani, T.; Kowalski, A.; Kudo, T.; Kurokawa,
T.; Kuzuhara, M.; Lin, A.; Maney, M.; Metcalf, A. J.; Morris, B.;
Nishikawa, J.; Omiya, M.; Robertson, P.; Roy, A.; Schwab, C.; Serizawa,
T.; Tamura, M.; Ueda, A.; Vievard, S.; Wisniewski, J.
Bibcode: 2021yCat..51620082K
Altcode:
We observed a photometric transit of TRAPPIST-1b on the night of UT
2020 September 5 using the Astrophysical Research Consortium Telescope
Imaging Camera (ARCTIC) on the 3.5m Astrophysical Research Consortium
Telescope at Apache Point Observatory. We adopted the SDSS filter using
an exposure time of 18s in the 4x4 binning fast-readout mode. We
observed the transit of TRAPPIST-1b on the night of UT 2020 September
17 using Infrared Doppler (IRD), which has a spectral resolution of
~70000 in the operating wavelength range of 0.95-1.75μm, mounted on the
8.2m Subaru Telescope on Maunakea, Hawaii. Habitable Planet Finder
(HPF) is a fiber-fed high-resolution (R=55000) spectrograph on the 10m
Hobby-Eberly Telescope (HET) at McDonald Observatory in Texas. Using
HPF, we obtained three transits on the nights of UT 2018 October 2,
2019 July 31, and 2020 September 5. (3 data files).
Title: A Search for Planetary Metastable Helium Absorption in the
V1298 Tau System
Authors: Vissapragada, Shreyas; Stefánsson, Gudmundur; Greklek-McKeon,
Michael; Oklopčić, Antonija; Knutson, Heather A.; Ninan, Joe P.;
Mahadevan, Suvrath; Cañas, Caleb I.; Chachan, Yayaati; Cochran,
William D.; Collins, Karen A.; Dai, Fei; David, Trevor J.; Halverson,
Samuel; Hawley, Suzanne L.; Hebb, Leslie; Kanodia, Shubham; Kowalski,
Adam F.; Livingston, John H.; Maney, Marissa; Metcalf, Andrew J.;
Morley, Caroline; Ramsey, Lawrence W.; Robertson, Paul; Roy, Arpita;
Spake, Jessica; Schwab, Christian; Terrien, Ryan C.; Tinyanont,
Samaporn; Vasisht, Gautam; Wisniewski, John
Bibcode: 2021AJ....162..222V
Altcode: 2021arXiv210805358V
Early in their lives, planets endure extreme amounts of ionizing
radiation from their host stars. For planets with primordial
hydrogen and helium-rich envelopes, this can lead to substantial
mass loss. Direct observations of atmospheric escape in young
planetary systems can help elucidate this critical stage of planetary
evolution. In this work, we search for metastable helium absorption-a
tracer of tenuous gas in escaping atmospheres-during transits of three
planets orbiting the young solar analog V1298 Tau. We characterize
the stellar helium line using HET/HPF, and find that it evolves
substantially on timescales of days to months. The line is stable
on hour-long timescales except for one set of spectra taken during
the decay phase of a stellar flare, where absoprtion increased with
time. Utilizing a beam-shaping diffuser and a narrowband filter
centered on the helium feature, we observe four transits with
Palomar/WIRC: two partial transits of planet d (P = 12.4 days), one
partial transit of planet b (P = 24.1 days), and one full transit of
planet c (P = 8.2 days). We do not detect the transit of planet c,
and we find no evidence of excess absorption for planet b, with ΔR
b/R ⋆ < 0.019 in our bandpass. We find
a tentative absorption signal for planet d with ΔR d/R
⋆ = 0.0205 ± 0.054, but the best-fit model requires a
substantial (-100 ± 14 minutes) transit-timing offset on a two-month
timescale. Nevertheless, our data suggest that V1298 Tau d may have
a high present-day mass-loss rate, making it a priority target for
follow-up observations.
Title: High-frequency Wave Power Observed in the Solar Chromosphere
with IBIS and ALMA
Authors: Molnar, Momchil E.; Reardon, Kevin P.; Cranmer, Steven R.;
Kowalski, Adam F.; Chai, Yi; Gary, Dale
Bibcode: 2021ApJ...920..125M
Altcode: 2021arXiv210708952M
We present observational constraints on the chromospheric heating
contribution from acoustic waves with frequencies between 5 and 50
mHz. We use observations from the Dunn Solar Telescope in New Mexico,
complemented with observations from the Atacama Large Millimeter Array
collected on 2017 April 23. The properties of the power spectra of the
various quantities are derived from the spectral lines of Ca II 854.2
nm, H I 656.3 nm, and the millimeter continuum at 1.25 and 3 mm. At
the observed frequencies, the diagnostics almost all show a power-law
behavior, whose particulars (slope, peak, and white-noise floors)
are correlated with the type of solar feature (internetwork, network,
and plage). In order to disentangle the vertical versus transverse
Alfvénic plasma motions, we examine two different fields of view: one
near disk center, and the other close to the limb. To infer the acoustic
flux in the middle chromosphere, we compare our observations with
synthetic observables from the time-dependent radiative hydrodynamic
RADYN code. Our findings show that acoustic waves carry up to about
1 kW m-2 of energy flux in the middle chromosphere, which
is not enough to maintain the quiet chromosphere. This is in contrast
to previous publications.
Title: Nondetection of Helium in the Upper Atmospheres of TRAPPIST-1b,
e, and f
Authors: Krishnamurthy, Vigneshwaran; Hirano, Teruyuki; Stefánsson,
Gumundur; Ninan, Joe P.; Mahadevan, Suvrath; Gaidos, Eric; Kopparapu,
Ravi; Sato, Bunei; Hori, Yasunori; Bender, Chad F.; Cañas, Caleb
I.; Diddams, Scott A.; Halverson, Samuel; Harakawa, Hiroki; Hawley,
Suzanne; Hearty, Fred; Hebb, Leslie; Hodapp, Klaus; Jacobson, Shane;
Kanodia, Shubham; Konishi, Mihoko; Kotani, Takayuki; Kowalski, Adam;
Kudo, Tomoyuki; Kurokawa, Takashi; Kuzuhara, Masayuki; Lin, Andrea;
Maney, Marissa; Metcalf, Andrew J.; Morris, Brett; Nishikawa, Jun;
Omiya, Masashi; Robertson, Paul; Roy, Arpita; Schwab, Christian;
Serizawa, Takuma; Tamura, Motohide; Ueda, Akitoshi; Vievard,
Sébastien; Wisniewski, John
Bibcode: 2021AJ....162...82K
Altcode: 2021arXiv210611444K
We obtained high-resolution spectra of the ultracool M-dwarf TRAPPIST-1
during the transit of its planet "b" using two high-dispersion
near-infrared spectrographs, the Infrared Doppler (IRD) instrument on
the Subaru 8.2m telescope, and the Habitable Zone Planet Finder (HPF)
instrument on the 10 m Hobby-Eberly Telescope. These spectroscopic
observations are complemented by a photometric transit observation
for planet "b" using the APO/ARCTIC, which assisted us in capturing
the correct transit times for our transit spectroscopy. Using the
data obtained by the new IRD and HPF observations, as well as the
prior transit observations of planets "b," "e" and "f" from IRD,
we attempt to constrain the atmospheric escape of the planet using
the He I triplet 10830 Å absorption line. We do not detect evidence
for any primordial extended H-He atmospheres in all three planets. To
limit any planet-related absorption, we place an upper limit on the
equivalent widths of <7.754 mÅ for planet "b," <10.458 mÅ for
planet "e," <4.143 mÅ for planet "f" at 95% confidence from the
IRD data, and <3.467 mÅ for planet "b" at 95% confidence from HPF
data. Using these limits along with a solar-like composition isothermal
Parker wind model, we attempt to constrain the mass-loss rates for the
three planets. For TRAPPIST-1b, our models exclude the highest possible
energy-limited rate for a wind temperature <5000 K. This nondetection
of extended atmospheres with low mean-molecular weights in all three
planets aids in further constraining their atmospheric composition by
steering the focus toward the search of high-molecular-weight species
in their atmospheres. *Based on data collected at Subaru
Telescope, operated by the National Astronomical Observatory of Japan,
Hobby-Eberly Telescope operated by The University of Texas McDonald
Observatory, and ARC 3.5m Telescope at Apache Point Observatory.
Title: The ESCAPE mission overview: exploring the stellar drivers
of exoplanet habitability
Authors: France, Kevin; Fleming, Brian; Youngblood, Allison; Mason,
James; Drake, Jeremy J.; Amerstorfer, Ute; Barstow, Martin; Bourrier,
Vincent; Champey, Patrick; Fossati, Luca; Froning, Cynthia; Green,
James C.; Grisé, Fabien; Gronoff, Guillaume; Hellickson, Timothy;
Jin, Meng; Koskinen, Tommi T.; Kowalski, Adam F.; Kruczek, Nicholas;
Linsky, Jeffrey L.; Lipscy, Sarah J.; McEntaffer, Randall L.; Miles,
Drew M.; Patton, Tom; Savage, Sabrina L.; Siegmund, Oswald; Spittler,
Constance; Unruh, Bryce; Volz, Márie
Bibcode: 2021SPIE11821E..03F
Altcode:
The Extreme-ultraviolet Stellar Characterization for Atmospheric
Physics and Evolution (ESCAPE) mission is an astrophysics Small
Explorer employing ultraviolet spectroscopy (EUV: 80 - 825 Å and FUV:
1280 - 1650 Å) to explore the high-energy radiation environment in
the habitable zones around nearby stars. ESCAPE provides the first
comprehensive study of the stellar EUV and coronal mass ejection
environments which directly impact the habitability of rocky
exoplanets. In a 20 month science mission, ESCAPE will provide the
essential stellar characterization to identify exoplanetary systems
most conducive to habitability and provide a roadmap for NASA's
future life-finder missions. ESCAPE accomplishes this goal with
roughly two-order-of-magnitude gains in EUV efficiency over previous
missions. ESCAPE employs a grazing incidence telescope that feeds an
EUV and FUV spectrograph. The ESCAPE science instrument builds on
previous ultraviolet and X-ray instrumentation, grazing incidence
optical systems, and photon-counting ultraviolet detectors used on
NASA astrophysics, heliophysics, and planetary science missions. The
ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace
BCP-Small spacecraft. Data archives will be housed at the Mikulski
Archive for Space Telescopes (MAST). ESCAPE is currently completing
a NASA Phase A study, and if selected for Phase B development would
launch in 2025.
Title: Time-resolved spectroscopy and photometry of an M dwarf flare
star YZ Canis Minoris with OISTER and TESS: Blue asymmetry in H-alpha
line during the non-white light flare
Authors: Maehara, Hiroyuki; Notsu, Yuta; Namekata, Kousuke; Honda,
Satoshi; Kowalski, Adam F.; Katoh, Noriyuki; Ohshima, Tomohito; Iida,
Kota; Oeda, Motoki; Murata, Katsuhiro L.; Yamanaka, Masayuki; Takagi,
Kengo; Sasada, Mahito; Akitaya, Hiroshi; Ikuta, Kai; Okamoto, Soshi;
Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2021tsc2.confE..16M
Altcode:
We report the results from spectroscopic and photometric observations
of the M-type flare star YZ CMi in the framework of the Optical and
Infrared Synergetic Telescopes for Education and Research (OISTER)
collaborations during the Transiting Exoplanet Survey Satellite (TESS)
observation period. We detected 4 H-alpha flares and one of them did
not show clear brightening in the continuum; during this flare, the
H-alpha line exhibited blue-asymmetry which has lasted for (\sim 60)
min. The line of sight velocity of the blue-shifted component is (\sim
-80) km/s. Under the assumption of that observed blue-asymmetry in
H-alpha line was caused by a prominence eruption, the mass and kinetic
energy of the upward-moving material are estimated to be (10^{16}) -
(10^{18}) g and (10^{29.5}) - (10^{31.5}) erg, respectively. Although
the estimated mass is comparable to expectations from the empirical
relation between the X-ray flare energy and mass of solar coronal mass
ejections (CMEs), the estimated kinetic energy is roughly 2 orders
of magnitude smaller than that expected from the relation for solar
CMEs. This discrepancy could be understood by the difference in the
velocity between CMEs and prominence eruptions (Maehara et al. 2021
PASJ, 73, 44).
Title: Blue asymmetries in Balmer lines during mid M dwarf flares
Authors: Notsu, Yuta; Kowalski, Adam F.; Maehara, Hiroyuki; Namekata,
Kosuke; Honda, Satoshi; Enoto, Teruaki; Hamaguchi, Kenji; Tristan,
Isaiah; Hawley, Suzanne L.; Davenport, James R. A.; Okamoto, Soshi;
Ikuta, Kai; Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2021tsc2.confE.118N
Altcode:
Flares are releases of magnetic energy in the stellar atmosphere, and
they have strong emissions from radio to X-rays. During some M dwarf
flares, chromospheric line profiles show blue asymmetries, although
red asymmetries are more commonly observed in solar flares. Similar
enhancements of the blue wings of Balmer lines may provide clues for
investigating the early phases of stellar coronal mass ejections (CMEs),
but this is still controversial. Thus, we need more observations to
understand the relationship between mass ejections and flares. We have
conducted simultaneous spectroscopic and photometric observations of
mid M dwarf flare stars using APO 3.5m/ARCES, SMARTS1.5m/CHIRON, TESS,
and etc. During 34 night observations, we detected 48 flares in Balmer
lines (e.g. Hα). At least 7 flares show clear blue asymmetries. Blue
asymmetry durations are different among the 7 events (20min ~
2hr). These results suggest upward flows of chromospheric plasma during
flare events. By assuming that the blue asymmetries were caused by
prominence eruptions, we estimated the mass and kinetic energy. The
estimated masses are comparable to expectations from the empirical
relation between the flare X-ray energy and mass of solar CMEs.
Title: Spectroscopic Study Of Wave Propagation In The Quiet Solar
Chromosphere with IRIS and IBIS
Authors: Molnar, M. E.; Cranmer, S. R.; Reardon, K. P.; Kowalski, A. F.
Bibcode: 2021AAS...23811303M
Altcode:
In this work, we present constraints on the longitudinal (compressive)
and transverse (Alfvenic) wave velocity perturbations observed in the
chromosphere. Better knowledge of the power in these different wave
modes in different regions of the atmosphere are important inputs into
models for the heating of the solar corona. By using observations
at multiple viewing angles (distances from the disc center), the
relative importance of these two components can be evaluated and
the power in the local acoustic flux can be explored. This work is
based on Doppler velocity measurements from IRIS of the ultraviolet
Mg II h & k and the Mn I 280.19 nm lines. These are compared with
co-temporal observations from IBIS of the H-alpha and Ca II 854.2 nm
chromospheric lines in the visible. The observed phase differences
between the velocity diagnostics in these different lines allows us to
estimate a formation height of the Mn I 280.19 nm line and compare it
with recent results from simulations. We can also measure the lowest
observed frequency at which the phase differences indicate the presence
of wave propagation in order to calculate the local acoustic-wave
cutoff. We calculate the coherency of the signals and their phases with
a cross-wavelet analysis. We further combine the IRIS observations
with 1D simulations of the lower solar atmosphere from the RADYN
code to estimate the wave flux inthe upper chromosphere. This study
provides heating constraints for the middle and upper chromospheres and
additional estimates of the transverse wave power in the chromosphere
extending previous work by Molnar et al. (2021).
Title: A Multiwavelength Exploration Of Galex And Kepler Flares
Authors: Brasseur, C.; Osten, R.; Tristan, I.; Kowalski, A.
Bibcode: 2021AAS...23820802B
Altcode:
Flares are the most dramatic energy release events that cool stars
will experience while on the main sequence. A result of magnetic
reconnection events, they are found on all solar-like stars to varying
degrees. I will present the results of our multiwavelength study
of flares found in data from the GALEX (NUV) and Kepler (optical)
missions. Multi-wavelength measurements enable estimation of the flare
increase at NUV wavelengths for flares without NUV measurements and
vice versa. I discuss our exploration of flare rates for the same
body of stars when observed in the optical vs NUV wavebands, and
our search for Kepler counterparts to the GALEX flares described in
Brasseur et al. 2019. I will present our evidence of excess emission
in the UV, the limitations we have been able to place on flare energy
fractionation between optical and UV, and possible physical mechanisms
behind these results.
Title: Impulsiveness Classification Scheme for Solar Flare Light
Curves in the He II 304 Å Chromospheric Line
Authors: Tamburri, C.; Kazachenko, M.; Kowalski, A.
Bibcode: 2021AAS...23812714T
Altcode:
The Solar Dynamics Observatory Extreme Ultraviolet Variability
Experiment (SDO/EVE) provides "Sun-as-a-star" data corresponding to
the variability of the Sun's irradiance in the XUV and EUV wavelengths
(from 0.1 to 106 nm). Using EVE light curves in the 304 Angstrom line,
we study 2049 solar flares from 2010 April 30 to 2014 May 26. We present
an algorithm for fitting the flare light curves in the 304 Angstrom
line, emitted by He II at around 50000 K from the chromosphere and
transition region and therefore representative of the dominant source
of radiation in a solar flare. We use this algorithm to identify
particularly high signal-to-noise flare light curves within the
database, with representatives from C, M, and X flare classes. The
parameters of the model associated with each flare can be used to
identify features such as secondary peaks in the decay phase. In
addition, we devise a morphological classification scheme based on
flare "impulsiveness" and apply the scheme to a sub-sample of the
flares. While a similar method has been used in the past to classify
stellar flares, it has yet to be extensively applied to solar flare
light curves. Morphological variations in flare development and their
relationship to impulsiveness are studied using SDO Atmospheric Imaging
Assembly (AIA) instrument data in the 1600 Angstrom line. A comparison
is made to several solar flare properties including duration, peak X-ray
flux, and quasi-periodic pulsation (QPP) period, among others. Using
the modeling algorithm and impulsiveness classification scheme in the
chromospheric 304 Angstrom line, it may be possible to identify and
study solar and stellar flare features not revealed by traditional
methods, particularly when Sun-as-a-star light curves are studied
together with full-disk images.
Title: A New View of the Solar Interface Region from the Interface
Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, Bart; Polito, Vanessa; Hansteen, Viggo; Testa,
Paola; Reeves, Katharine K.; Antolin, Patrick; Nóbrega-Siverio,
Daniel Elias; Kowalski, Adam F.; Martinez-Sykora, Juan; Carlsson,
Mats; McIntosh, Scott W.; Liu, Wei; Daw, Adrian; Kankelborg, Charles C.
Bibcode: 2021SoPh..296...84D
Altcode: 2021arXiv210316109D
The Interface Region Imaging Spectrograph (IRIS) has been obtaining
near- and far-ultraviolet images and spectra of the solar atmosphere
since July 2013. IRIS is the highest resolution observatory to provide
seamless coverage of spectra and images from the photosphere into the
low corona. The unique combination of near- and far-ultraviolet spectra
and images at sub-arcsecond resolution and high cadence allows the
tracing of mass and energy through the critical interface between the
surface and the corona or solar wind. IRIS has enabled research into the
fundamental physical processes thought to play a role in the low solar
atmosphere such as ion-neutral interactions, magnetic reconnection, the
generation, propagation, and dissipation of waves, the acceleration of
non-thermal particles, and various small-scale instabilities. IRIS has
provided insights into a wide range of phenomena including the discovery
of non-thermal particles in coronal nano-flares, the formation and
impact of spicules and other jets, resonant absorption and dissipation
of Alfvénic waves, energy release and jet-like dynamics associated
with braiding of magnetic-field lines, the role of turbulence and the
tearing-mode instability in reconnection, the contribution of waves,
turbulence, and non-thermal particles in the energy deposition during
flares and smaller-scale events such as UV bursts, and the role of flux
ropes and various other mechanisms in triggering and driving CMEs. IRIS
observations have also been used to elucidate the physical mechanisms
driving the solar irradiance that impacts Earth's upper atmosphere,
and the connections between solar and stellar physics. Advances in
numerical modeling, inversion codes, and machine-learning techniques
have played a key role. With the advent of exciting new instrumentation
both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST)
and the Atacama Large Millimeter/submillimeter Array (ALMA), and
space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim
to review new insights based on IRIS observations or related modeling,
and highlight some of the outstanding challenges.
Title: Reconstructing the Extreme Ultraviolet Emission of Cool Dwarfs
Using Differential Emission Measure Polynomials
Authors: Duvvuri, Girish M.; Sebastian Pineda, J.; Berta-Thompson,
Zachory K.; Brown, Alexander; France, Kevin; Kowalski, Adam F.;
Redfield, Seth; Tilipman, Dennis; Vieytes, Mariela C.; Wilson, David
J.; Youngblood, Allison; Froning, Cynthia S.; Linsky, Jeffrey; Parke
Loyd, R. O.; Mauas, Pablo; Miguel, Yamila; Newton, Elisabeth R.;
Rugheimer, Sarah; Christian Schneider, P.
Bibcode: 2021ApJ...913...40D
Altcode: 2021arXiv210208493D
Characterizing the atmospheres of planets orbiting M dwarfs requires
understanding the spectral energy distributions of M dwarfs over
planetary lifetimes. Surveys like MUSCLES, HAZMAT, and FUMES have
collected multiwavelength spectra across the spectral type's range
of Teff and activity, but the extreme ultraviolet (EUV,
100-912 Å) flux of most of these stars remains unobserved because
of obscuration by the interstellar medium compounded with limited
detector sensitivity. While targets with observable EUV flux exist,
there is no currently operational facility observing between 150 and 912
Å. Inferring the spectra of exoplanet hosts in this regime is critical
to studying the evolution of planetary atmospheres because the EUV
heats the top of the thermosphere and drives atmospheric escape. This
paper presents our implementation of the differential emission measure
technique to reconstruct the EUV spectra of cool dwarfs. We characterize
our method's accuracy and precision by applying it to the Sun and AU
Mic. We then apply it to three fainter M dwarfs: GJ 832, Barnard's star,
and TRAPPIST-1. We demonstrate that with the strongest far-ultraviolet
(FUV, 912-1700 Å) emission lines, observed with the Hubble Space
Telescope and/or Far Ultraviolet Spectroscopic Explorer, and a coarse
X-ray spectrum from either the Chandra X-ray Observatory or XMM-Newton,
we can reconstruct the Sun's EUV spectrum to within a factor of 1.8,
with our model's formal uncertainties encompassing the data. We report
the integrated EUV flux of our M dwarf sample with uncertainties of
a factor of 2-7 depending on available data quality.
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
Bibcode: 2021SoPh..296...70R
Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
Title: The Mega-MUSCLES Spectral Energy Distribution of TRAPPIST-1
Authors: Wilson, David J.; Froning, Cynthia S.; Duvvuri, Girish
M.; France, Kevin; Youngblood, Allison; Schneider, P. Christian;
Berta-Thompson, Zachory; Brown, Alexander; Buccino, Andrea P.; Hawley,
Suzanne; Irwin, Jonathan; Kaltenegger, Lisa; Kowalski, Adam; Linsky,
Jeffrey; Parke Loyd, R. O.; Miguel, Yamila; Pineda, J. Sebastian;
Redfield, Seth; Roberge, Aki; Rugheimer, Sarah; Tian, Feng; Vieytes,
Mariela
Bibcode: 2021ApJ...911...18W
Altcode: 2021arXiv210211415W
We present a 5 Å-100 μm spectral energy distribution (SED)
of the ultracool dwarf star TRAPPIST-1, obtained as part of
the Mega-MUSCLES Treasury Survey. The SED combines ultraviolet
and blue-optical spectroscopy obtained with the Hubble Space
Telescope, X-ray spectroscopy obtained with XMM-Newton, and models
of the stellar photosphere, chromosphere, transition region, and
corona. A new differential emission measure model of the unobserved
extreme-ultraviolet spectrum is provided, improving on the Lyα-EUV
relations often used to estimate the 100-911 Å flux from low-mass
stars. We describe the observations and models used, as well as the
recipe for combining them into an SED. We also provide a semiempirical,
noise-free model of the stellar ultraviolet spectrum based on our
observations for use in atmospheric modeling of the TRAPPIST-1 planets.
Title: Erratum: Optical and X-ray observations of stellar flares
on an active M dwarf AD Leonis with Seimei Telescope, SCAT, NICER,
and OISTER
Authors: Namekata, Kosuke; Maehara, Hiroyuki; Sasaki, Ryo; Kawai,
Hiroki; Notsu, Yuta; Kowalski, Adam F.; Allred, Joel C.; Iwakiri,
Wataru; Tsuboi, Yoko; Murata, Katsuhiro L.; Niwano, Masafumi;
Shiraishi, Kazuki; Adachi, Ryo; Iida, Kota; Oeda, Motoki; Honda,
Satoshi; Tozuka, Miyako; Katoh, Noriyuki; Onozato, Hiroki; Okamoto,
Soshi; Isogai, Keisuke; Kimura, Mariko; Kojiguchi, Naoto; Wakamatsu,
Yasuyuki; Tampo, Yusuke; Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2021PASJ...73..485N
Altcode: 2021PASJ..tmp...16N
No abstract at ADS
Title: Discovery of an Extremely Short Duration Flare from Proxima
Centauri Using Millimeter through Far-ultraviolet Observations
Authors: MacGregor, Meredith A.; Weinberger, Alycia J.; Loyd,
R. O. Parke; Shkolnik, Evgenya; Barclay, Thomas; Howard, Ward S.;
Zic, Andrew; Osten, Rachel A.; Cranmer, Steven R.; Kowalski, Adam
F.; Lenc, Emil; Youngblood, Allison; Estes, Anna; Wilner, David J.;
Forbrich, Jan; Hughes, Anna; Law, Nicholas M.; Murphy, Tara; Boley,
Aaron; Matthews, Jaymie
Bibcode: 2021ApJ...911L..25M
Altcode: 2021arXiv210409519M
We present the discovery of an extreme flaring event from Proxima
Cen by the Australian Square Kilometre Array Pathfinder (ASKAP),
Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space
Telescope (HST), Transiting Exoplanet Survey Satellite (TESS), and
the du Pont Telescope that occurred on 2019 May 1. In the millimeter
and FUV, this flare is the brightest ever detected, brightening
by a factor of >1000 and >14,000 as seen by ALMA and HST,
respectively. The millimeter and FUV continuum emission trace each
other closely during the flare, suggesting that millimeter emission
could serve as a proxy for FUV emission from stellar flares and become
a powerful new tool to constrain the high-energy radiation environment
of exoplanets. Surprisingly, optical emission associated with the event
peaks at a much lower level with a time delay. The initial burst has
an extremely short duration, lasting for <10 s. Taken together with
the growing sample of millimeter M dwarf flares, this event suggests
that millimeter emission is actually common during stellar flares and
often originates from short burst-like events.
Title: Discovery of an Extremely Short Duration 'Building Block'
Flare from Proxima Centauri
Authors: MacGregor, M.; Weinberger, A.; Loyd, P.; Shkolnik, E.;
Barclay, T.; Howard, W.; Zic, A.; Osten, R.; Cranmer, S.; Kowalski,
A.; Lenc, E.; Youngblood, A.; Estes, A.; Wilner, D.; Forbrich, J.;
Hughes, A.; Law, N.; Murphy, T.; Boley, A.; Matthews, J.
Bibcode: 2021BAAS...53c1249M
Altcode:
At a distance of only 1.3 pc, Proxima Cen is the closest exoplanetary
system orbiting an M-type flare star, making it a benchmark case to
explore the properties and potential effects of stellar activity on
exoplanet atmospheres. Here, we present the discovery of an extreme
flaring event from Proxima Cen by the the Australian Square Kilometre
Array Pathfinder (ASKAP), the Atacama Large Millimeter/submillimeter
Array (ALMA), the Transiting Exoplanet Survey Satellite (TESS), the
du Pont telescope at Las Campanas, and the Hubble Space Telescope
(HST). In the millimeter and FUV, this flare is the brightest ever
detected, brightening by a factor of >1000 and >14000 as seen by
ALMA and HST, respectively. The millimeter and FUV continuum emission
trace each other closely during the flare, suggesting that millimeter
emission could serve as a proxy for FUV emission from stellar flares
and become a powerful new tool to constrain the high-energy radiation
environment of exoplanets. Optical emission is decoupled, peaking at
a much lower level with a time delay. The extremely short duration
of this event indicates that it could originate from a single flare
loop or 'building block.' These are the first results from a larger
campaign executed in April-July 2019 consisting of roughly 40 hours
of simultaneous observations of Proxima Cen spanning radio to X-ray
wavelengths.
Title: Blue asymmetries in Balmer lines during mid M dwarf flares
Authors: Notsu, Yuta; Kowalski, Adam F.; Maehara, Hiroyuki; Namekata,
Kosuke; Honda, Satoshi; Enoto, Teruaki; Hamaguchi, Kenji; Tristan,
Isaiah; Hawley, Suzanne L.; Davenport, James R. A.; Okamoto, Soshi;
Ikuta, Kai; Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2021csss.confE.103N
Altcode:
Flares are releases of magnetic energy in the solar/stellar atmosphere,
and they have strong emissions from radio to X-rays. During some
M dwarf flares, chromospheric line profiles show blue asymmetries
(Eason et al. 1992; Honda et al. 2018), although red asymmetries are
more commonly observed in solar flares. Similar enhancements of the
blue wings of Balmer lines may provide clues for investigating the
early phases of stellar coronal mass ejections (CMEs) during flares
(cf. Vida et al. 2016&2019), but this is still controversial. Thus,
we need more flare spectroscopic observations with high time resolution
to understand the relationship between mass ejections and flaring
events. The latter is helpful for estimating the impact on planets
from flares.We have conducted several simultaneous spectroscopic
and photometric observations of mid M dwarf flare stars using
APO 3.5m/ARCES, SMARTS 1.5m/CHIRON, TESS, and ground- based 0.4-1m
photometric telescopes. During 34 nights of observations, we detected
48 flares in Balmer lines (e.g. H-alpha). Among them, at least 7
flare events show clear blue asymmetries. Blue asymmetry durations
are different among the 7 events (20min ~ 2hr).These results suggest
upward flows of chromospheric plasma during flare events. By assuming
that the blue asymmetries were caused by prominence eruptions, we
estimate the mass and kinetic energy of the upward-moving material
to be 1015 - 1018 g and 1029 -
1032 erg, respectively. The estimated masses are comparable
to expectations from the empirical relation between the flare X-ray
energy and mass of upward-moving material for stellar flares and
solar CMEs. In contrast, the estimated kinetic energies for these
non-white-light flares are roughly 2-3 orders of magnitude smaller than
that expected from the relation between flare X-ray energy and kinetic
energy for solar CMEs. This could be understood by the difference in
the velocity between CMEs and prominence eruptions.
Title: Redefining the Neupert Effect in M Dwarfs through
Multi-Wavelength Timing Analysis of AU Mic's Flares
Authors: Tristan, Isaiah I.; Notsu, Yuta; Kowalski, Adam F.; Brown,
Alexander; Vrijmoet, Eliot H.; Allred, Joel C.; Carter, Brad D.; Grady,
Carol A.; Henry, Todd J.; Hinojosa, Rodrigo H.; Jao, Wei-Chun; Lomax,
Jamie R.; Neff, James E.; Osten, Rachel A.; Paredes, Leonardo A.;
Schneider, Glenn H.; Soutter, Jack; White, Graeme L.; Wisniewski,
John P.
Bibcode: 2021csss.confE.123T
Altcode:
M dwarfs are considered one of the most likely places to find
extraterrestrial life in part due to their large numbers in the
nearby solar neighborhood. However, they have much more intense
flaring events than stars like our Sun, which could negatively impact
the habitability of close-in exoplanets. Our current understanding
of the multi-wavelength connections of M dwarf flaring events is
surprisingly far from complete, both in wavelength coverage and temporal
resolution. To rectify this, our team collected multi-wavelength
data of the dM1e flare star AU Mic over 7-days using a variety
of telescopes. Here, we focus on data from XMM-Newton and the Las
Cumbres Observatory Global Telescope (LCOGT) network. We discuss the
Neupert effect among the X-ray, UV, and optical response in a sample of
high-energy flares and present cumulative flare frequency distribution
(CFFD) statistics. We find that AU Mic's U-band CFFD is consistent with
other M dwarfs in the literature and that the Neupert effect (i.e. the
X-ray derivative peak and NUV peak timings overlap) is not present
in all characterized flares. We propose a new Neupert classification
system that includes Quasi-Neupert (response in X-ray and NUV, but the
timings do not match) and Non-Neupert (missing a response from either
X-ray or NUV). Future work on this project includes adding existing
AU Mic radio and H-alpha observations to our analysis and using our
RADYN flare modeling program to determine the electron beam heating,
proton beam heating, and magnetic mirroring needed to reproduce the
full range of multi-wavelength responses we see in observations.
Title: Time-resolved spectroscopy and photometry of an M dwarf flare
star YZ Canis Minoris with OISTER and TESS: Blue asymmetry in H\alpha
line during the non-white light flare
Authors: Maehara, Hiroyuki; Notsu, Yuta; Namekata, Kousuke; Honda,
Satoshi; Kowalski, Adam F.; Katoh, Noriyuki; Ohshima, Tomohito; Iida,
Kota; Oeda, Motoki; Murata, Katsuhiro L.; Yamanaka, Masayuki; Takagi,
Kengo; Sasada, Mahito; Akitaya, Hiroshi; Ikuta, Kai; Okamoto, Soshi;
Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2021csss.confE.142M
Altcode:
Flares are thought to be the rapid releases of magnetic energy through
magnetic reconnection in the corona. Blue asymmetries (enhancement of
the blue wing) in chromospheric lines have been widely observed during
flares on M dwarfs. They are thought to be caused by the upward motions
of cool plasma (e.g., chromospheric evaporations, filament/prominence
eruptions). As observed on the Sun, stellar filament/prominence
eruptions can evolve into stellar CMEs (coronal mass ejections).Here
we report the results from spectroscopic and photometric observations
of the M-type flare star YZ CMi in the framework of the Optical and
Infrared Synergetic Telescopes for Education and Research (OISTER)
collaborations during the Transiting Exoplanet Survey Satellite
(TESS) observation period.We detected 145 white-light flares from the
TESS light curve and 4 H(\alpha) flares from the OISTER observations
performed between 2019-01-16 and 2019-01-18. Among them, 3 H(\alpha)
flares were associated with white-light flares. However, one of them
did not show clear brightening in continuum; during this flare, the
H(\alpha) line exhibited blue-asymmetry which has lasted for (\sim
60) min. The line of sight velocity of the blue-shifted component is
(-80) - (-100) km s-1. By assuming that the blue-asymmetry
in H(\alpha) line was caused by a prominence eruption on YZ CMi, we
estimated the mass and kinetic energy of the upward-moving material
to be (10^{16}) - (10^{18}) g and (10^{29.5}) - (10^{31.5}) erg,
respectively.Although, the estimated mass is comparable to expectations
from the empirical relation between the flare X-ray energy and mass of
upward-moving material for solar CMEs, the estimated kinetic energy for
the non-white-light flare on YZ CMi is roughly 2 orders of magnitude
smaller than that expected from the relation between flare X-ray energy
and kinetic energy for solar CMEs. This could be understood by the
difference in the velocity between CMEs and prominence eruptions.
Title: Time-resolved spectroscopy and photometry of M dwarf flare
star YZ Canis Minoris with OISTER and TESS: Blue asymmetry in the
Hα line during the non-white light flare
Authors: Maehara, Hiroyuki; Notsu, Yuta; Namekata, Kousuke; Honda,
Satoshi; Kowalski, Adam F.; Katoh, Noriyuki; Ohshima, Tomohito; Iida,
Kota; Oeda, Motoki; Murata, Katsuhiro L.; Yamanaka, Masayuki; Takagi,
Kengo; Sasada, Mahito; Akitaya, Hiroshi; Ikuta, Kai; Okamoto, Soshi;
Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2021PASJ...73...44M
Altcode: 2020PASJ..tmp..253M; 2020arXiv200914412M
In this paper, we present the results from spectroscopic and photometric
observations of the M-type flare star YZ CMi in the framework of the
Optical and Infrared Synergetic Telescopes for Education and Research
(OISTER) collaborations during the Transiting Exoplanet Survey
Satellite (TESS) observation period. We detected 145 white-light
flares from the TESS light-curve and four Hα flares from the OISTER
observations performed between 2019 January 16 and 18. Among them,
three Hα flares were associated with white-light flares. However,
one of them did not show clear brightening in the continuum; during
this flare, the Hα line exhibited blue asymmetry which lasted for
∼60 min. The line-of-sight velocity of the blueshifted component is
in the range from -80 to -100 km s-1. This suggests that
there can be upward flows of chromospheric cool plasma even without
detectable red/near-infrared (NIR) continuum brightening. By assuming
that the blue asymmetry in the Hα line was caused by a prominence
eruption on YZ CMi, we estimated the mass and kinetic energy of the
upward-moving material to be 1016-1018 g and
1029.5-1031.5 erg, respectively. The estimated
mass is comparable to expectations from the empirical relation between
the flare X-ray energy and mass of upward-moving material for stellar
flares and solar coronal mass ejections (CMEs). In contrast, the
estimated kinetic energy for the non-white-light flare on YZ CMi is
roughly two orders of magnitude smaller than that expected from the
relation between flare X-ray energy and kinetic energy for solar
CMEs. This could be understood by the difference in the velocity
between CMEs and prominence eruptions.
Title: Blue asymmetries in Balmer lines during mid M dwarf flares
Authors: Notsu, Y.; Kowalski, A.; Maehara, H.; Namekata, K.; Honda,
S.; Enoto, T.; Hamaguchi, K.; Tristan, I.; Hawley, S.; Davenport,
J.; Okamoto, S.; Ikuta, K.; Nogami, D.; Shibata, K.
Bibcode: 2021AAS...23751501N
Altcode:
Flares are releases of magnetic energy in the solar/stellar atmosphere,
and they have strong emissions from radio to X-rays. During some
M dwarf flares, chromospheric line profiles show blue asymmetries
(Honda et al. 2018), although red asymmetries are more commonly
observed in solar flares. Similar enhancements of the blue wings of
Balmer lines may provide clues for investigating the early phases
of stellar coronal mass ejections (CMEs) during flares (cf. Vida et
al. 2016&2019), but this is still controversial. Thus, we need
more flare spectroscopic observations with high time resolution
to understand the relationship between mass ejections and flaring
events. The latter is helpful for estimating the impact on planets
from flares. We have conducted several simultaneous spectroscopic
and photometric observations of mid M dwarf flare stars using APO
3.5m/ARCES, SMARTS 1.5m/CHIRON, Nayuta 2m/MALLS (high-dispersion
spectroscopy), TESS (space high-precision single-color photometry),
and ground-based 0.4-1m telescopes (ground-based photometry). During
~20 nights of observations, we detected more than 30 flares in Balmer
lines (e.g. Hα). Among them, at least 6 flare events (including one
already reported in Maehara et al. 2020) show clear blue asymmetries,
but none show brightening in the continuum. Blue asymmetry durations are
different among the 6 events (20min ~ 2hr). These results suggest upward
flows of chromospheric plasma during "non-white light" flare events. By
assuming that the blue asymmetries were caused by prominence eruptions,
we estimate the mass and kinetic energy of the upward-moving material to
be 1015-1018 g and 1029-1032
erg, respectively. The estimated masses are comparable to expectations
from the empirical relation between the flare X-ray energy and mass of
upward-moving material for stellar flares and solar CMEs. In contrast,
the estimated kinetic energies for these non-white-light flares are
roughly 2 orders of magnitude smaller than that expected from the
relation between flare X-ray energy and kinetic energy for solar
CMEs. This could be understood by the difference in the velocity
between CMEs and prominence eruptions.
Title: Superflares investigated with Kepler&TESS photometric
data and recent multi-wavelength campaign observations
Authors: Notsu, Yuta; Shibata, Kazunari; Enoto, Teruaki; Hamaguchi,
Kenji; Honda, Satoshi; Maehara, Hiroyuki; Nogami, Daisaku; Namekata,
Kosuke; Ikuta, Kai; Kowalski, Adam; Hawley, Suzanne; Davenport, James;
Okamoto, Soshi; Notsu, Shota
Bibcode: 2021cosp...43E1750N
Altcode:
Solar flares are frequent energetic explosions in the solar atmosphere,
and are thought to occur by impulsive releases of magnetic energy
stored around sunspots. Large solar flares sometimes can have large
impacts on our Earth and society (e.g., magnetic storms). Stars other
than the Sun also show flares. Many young stars, active M-dwarfs known
as flare stars, and close binary stars have ``superflares'', which are
flares that have a total energy 10--10$^{6}$ times larger than that of
the largest solar flares on the Sun ($\sim$10$^{32}$ erg). These stars
generally rotate very fast (Period $\sim$ 2--3 days). In contrast, the
Sun slowly rotates (Period $\sim$25 days). Then it had been thought that
superflares cannot occur on slowly-rotating G-type main-sequence stars
like the Sun. Recently, more than 1000 superflares on solar-type stars
(G-type main sequence stars) have been found using the photometric
data of Kepler spece telescope (and also TESS satellite). Using these
large number of data, it is now possible to do statistical studies
of superflares on solar-type stars. First, superflare stars are well
characterized by the existence of large starspots on the surface,
and their magnetic fluxes can explain well superflare energies. Then,
maximum superflare energy continuously decreases as the rotation period
increases. Superflares with their energy $\le \sim$ 5$\times$10$^{34}$
erg (a few hundred times larger than the largest solar flares) would
occur on old slowly-rotating Sun-like stars (Rotation Period $\sim$25
days) once every 2000-3000 years, while young rapidly-rotating
stars with Rotation Period $\sim$ a few days have superflares up
to 10$^{36}$ erg. These results presented in this work support that
even slowly-rotating stars similar to the Sun can have superflares,
considering long-term activity level changes. In addition to these
photometric observation results of solar-type superflare stars, cool
M-dwarf superflare stars have been investigated in more detail by
recent multi-wavelength surveys. For example, Hydrogen chromospheric
lines during flares show a lot of blue-shifted profiles, which can give
us some hints on dynamics or mass ejections during superflares. In
the main part of this review talk, I review the recent statistical
results of superflares from Kepler\&TESS data. Then in the latter
part, I also briefly discuss the results of recent multi-wavelength
campaign observations of M-dwarf superflares, and finally show the
future prospects of superflare studies, which are closely related with
solar physics and studies of effects on planets.
Title: Out of Sync: Redefining the Neupert Effect in M Dwarfs through
Multi-Wavelength Timing Analysis of AU Mic's Flares
Authors: Tristan, I. I.; Notsu, Y.; Kowalski, A. F.; Brown, A.;
Vrijmoet, E. H.; Allred, J. C.; Carter, B. D.; Grady, C. A.; Henry,
T. J.; Hinojosa, R. H.; Jao, W.; Lomax, J. R.; Neff, J. E.; Osten,
R. A.; Paredes, L. A.; Schneider, G. H.; Soutter, J.; White, G. L.;
Wisniewski, J. P.
Bibcode: 2021AAS...23755002T
Altcode:
M dwarfs are considered one of the most likely places to find
extraterrestrial life in part due to their large numbers in the
nearby solar neighborhood. However, they have much more intense
flaring events than stars like our Sun, which could negatively impact
the habitability of close-in exoplanets. Our current understanding
of the multi-wavelength connections of M dwarf flaring events is
surprisingly far from complete, both in wavelength coverage and temporal
resolution. To rectify this, our team collected multi-wavelength
data of the dM1e flare star AU Mic over 7-days with the Neil Gehrels
Swift Observatory, XMM-Newton, the Las Cumbres Observatory Global
Telescope (LCOGT) network, the Small and Moderate Aperture Telescope
Research System (SMARTS) 0.9m and 1.5m telescopes at the Cerro Tololo
Inter-American Observatory, the ARC 3.5m at APO, the ATCA, and the
Jansky Very Large Array. Here we discuss the Neupert effect among the
X-ray, UV, and optical response in a sample of high-energy flares. We
present high time-resolution light curves, flare correlations across
the spectrum, and cumulative flare frequency distribution (CFFD)
statistics. We find that AU Mic's U-band CFFD is consistent with other
M dwarfs in the literature, that the Neupert effect (i.e. the X-ray
derivative peak and NUV peak timings overlap) is not present in all
characterized flares, and that while timing differences between the U
and UVW2 flare peaks are small (<2 min.), their decay timings are
not always similar. We propose a new Neupert classification system that
includes Quasi-Neupert (response in X-ray and NUV, but the timings
do not match) and Non-Neupert (missing a response from either X-ray
or NUV). Future work on this project includes adding existing AU Mic
radio and Hα observations to our analysis and using our RADYN flare
modeling program to determine the electron beam heating, proton beam
heating, and magnetic mirroring needed to reproduce the full range of
multi-wavelength responses we see in observations.
Title: Discovery of an Extremely Short Duration 'Building Block'
Flare from Proxima Cen Using Millimeter through FUV Observations
Authors: MacGregor, M. A.; Weinberger, A. J.; Loyd, P.; Shkolnik,
E. L.; Barclay, T.; Osten, R.; Howard, W. S.; Zic, A.; Cranmer, S. R.;
Kowalski, A. F.; Youngblood, A.; Estes, A.; Wilner, D. J.; Forbrich,
J.; Murphy, T.; Law, N.; Hughes, A.; Boley, A.; Tristan, I. I.; Fuson,
J. F.; Matthews, J.
Bibcode: 2021AAS...23751502M
Altcode:
At a distance of only 1.3 pc, Proxima Cen is the closest exoplanetary
system orbiting an M-type flare star, making it a benchmark
case to explore the properties and potential effects of stellar
activity on exoplanet atmospheres. Our previous discovery of a flare
from Proxima Cen at millimeter wavelengths with the Atacama Large
Millimeter/submillimeter Array (ALMA) has opened up an entirely new
observational regime to study stellar flaring mechanisms. These are the
first results from a larger campaign consisting of roughly 40 hours of
simultaneous observations spanning radio to X-ray wavelengths. Here,
we present the discovery of a second flaring event on 1 May 2019 from
Proxima Cen with ALMA, but this time complemented by multi-wavelength
observations with the Hubble Space Telescope (HST) of far-ultraviolet
(FUV) spectroscopy, the Transiting Exoplanet Survey Satellite (TESS)
of optical photometry, and the DuPont telescope at Las Campanas of
optical spectroscopy. In the millimeter and FUV, the May 1 flare is
the brightest ever detected from Proxima Cen, brightening by a factor
of >1000 and >14000 as seen by ALMA and HST, respectively. The
millimeter and FUV continuum emission trace each other very closely
during the flare, exhibiting similar rise and decay times, peaking near
simultaneously, and achieving large enhancements in luminosity. Optical
emission is somewhat decoupled, peaking at a much lower level with
a slight time delay. Given the unique characteristics of this event,
it is possible that we are seeing an entirely new type of flare. The
extremely short duration of this event suggests that it could
originate from a single flare loop or 'building block' instead of an
arcade structure consisting of multiple superimposed loops. The strong
correlation between millimeter and FUV emission allows us to determine
a tentative scaling relation. If this holds for a larger sample of
events, millimeter emission could serve as a proxy for FUV emission
from stellar flares and become a powerful new tool to constrain the
high energy radiation environment of planets orbiting flare stars,
required input for models of planetary atmosphere evolution.
Title: Constraining wave propagation throughout the solar atmosphere
with IBIS, ALMA and IRIS
Authors: Molnar, M.; Reardon, K.; Cranmer, S. R.; Kowalski, A. F.
Bibcode: 2020AGUFMSH0010003M
Altcode:
The heating mechanism of the solar chromosphere is still an open
scientific question. We present observational constraints on the
high-frequency (acoustic) wave contribution to the chromospheric
heating. We utilize a unique combination of observations from NSO's
Dunn Solar Telescope and the Atacama Large Millimeter Array obtained on
April 23rd 2017 to estimate the high-frequency wave flux in the lower
solar atmosphere. We extend this study to the upper chromosphere and
the transition region with archival IRIS data. We infer the wave flux
through comparison of the observations with synthetic observables
from the time-dependent hydrodynamic RADYN code. Our findings are
able to constrain the wave flux at higher altitudes in the solar
atmosphere than previous works using similar approaches. Furthermore,
the different diagnostics we use form at different heights, which
allow us to explore the propagation and dissipation of waves with
height. We will discuss future plans to extend this work with more
advanced modeling and additional observations with the upcoming Innoue
Solar Telescope (DKIST).
Title: FP: A Fokker-Planck solver for modeling the transport of
flare-accelerated particles
Authors: Allred, J. C.; Alaoui, M.; Kowalski, A. F.; Kerr, G. S.
Bibcode: 2020AGUFMSH0500010A
Altcode:
We present a new open-source computational model, FP, that solves the
Fokker Planck equation to model the transport of flare-accelerated
particles at the top of magnetic flux loops to their eventual
thermalization in the footpoints. Our technique includes forces
corresponding to Coulomb collisions including second order energy
diffusion and pitch-angle diffusion, magnetic mirroring, synchrotron
emission and, critically, energy loss due to the return current electric
field. It is applicable to particles of arbitrary mass and charge. In
the case of nonthermal electrons, FP predicts the bremsstrahlung
produced as they collide with the ambient solar atmosphere. We have
incorporated FP into the OSPEX X-ray spectral analysis tool. We
use OSPEX+FP to fit X-ray spectra observed by RHESSI to constrain
nonthermal electron distributions in the SOL2013-05-13T16:01 X-class
solar flare. This flare shows a large spectral break, likely indicating
the effect of the return current electric field on nonthermal electrons.
Title: High-Cadence DST/ROSA Observations of the NUV/Blue Continuum
Radiation in a Solar Flare
Authors: Kowalski, A. F.; Keys, P.; Mathioudakis, M.
Bibcode: 2020AGUFMSH0500011K
Altcode:
Radiative-hydrodynamic models of solar flares provide sophisticated
predictions of the ultraviolet and optical continuum shape and
strength on shorter than 1 s timescales covering a broad wavelength
range. However, most optical observations of solar flares in the
modern era are not obtained at fast cadence and are not optimized
at blue continuum wavelengths, which provide a critical constraint
on the heating properties at large column mass. To rectify this
major gap in our knowledge of solar flare spectra, custom Balmer
jump filters were designed for the ROSA instrument at the Dunn Solar
Telescope. Unprecedented observations at 7.5 - 30 frames per second
were obtained covering the C9.7 flare SOL20141025T15:52 in NOAA AR
12192 during the NSO's Service Mode operations (and provided by the
F-CHROMA solar flare database). We report on how the flare response in
the 350 nm and 417 nm ROSA filters constrains several common assumptions
employed in modern flare modeling, such as the duration of individual
heating bursts. We also report on the Balmer jump properties in this
flare and compare to several M dwarf flares, which have been observed
in identical filters using the ULTRACAM and ARCTIC instruments on the
4.2m WHT, the 3.6m NTT, and the 3.5m ARC telescope. We compare the
light curves to radiative-hydrodynamic model predictions of the 350
nm brightness evolution on short timescales.
Title: The High-energy Radiation Environment around a 10 Gyr M Dwarf:
Habitable at Last?
Authors: France, Kevin; Duvvuri, Girish; Egan, Hilary; Koskinen, Tommi;
Wilson, David J.; Youngblood, Allison; Froning, Cynthia S.; Brown,
Alexander; Alvarado-Gómez, Julián D.; Berta-Thompson, Zachory K.;
Drake, Jeremy J.; Garraffo, Cecilia; Kaltenegger, Lisa; Kowalski,
Adam F.; Linsky, Jeffrey L.; Loyd, R. O. Parke; Mauas, Pablo J. D.;
Miguel, Yamila; Pineda, J. Sebastian; Rugheimer, Sarah; Schneider,
P. Christian; Tian, Feng; Vieytes, Mariela
Bibcode: 2020AJ....160..237F
Altcode: 2020arXiv200901259F
Recent work has demonstrated that high levels of X-ray and UV activity
on young M dwarfs may drive rapid atmospheric escape on temperate,
terrestrial planets orbiting within the habitable zone. However,
secondary atmospheres on planets orbiting older, less active M
dwarfs may be stable and present more promising candidates for
biomarker searches. In order to evaluate the potential habitability
of Earth-like planets around old, inactive M dwarfs, we present new
Hubble Space Telescope and Chandra X-ray Observatory observations of
Barnard&'s Star (GJ 699), a 10 Gyr old M3.5 dwarf, acquired as part
of the Mega-MUSCLES program. Despite the old age and long rotation
period of Barnard&'s Star, we observe two FUV (δ130
≍ 5000 s; E130 ≍ 1029.5 erg each) and one
X-ray (EX ≍ 1029.2 erg) flares, and we estimate
a high-energy flare duty cycle (defined here as the fraction of the
time the star is in a flare state) of ∼25%. A publicly available
5 Å to 10 μm spectral energy distribution of GJ 699 is created
and used to evaluate the atmospheric stability of a hypothetical,
unmagnetized terrestrial planet in the habitable zone (rHZ
∼ 0.1 au). Both thermal and nonthermal escape modeling indicate (1)
the quiescent stellar XUV flux does not lead to strong atmospheric
escape: atmospheric heating rates are comparable to periods of high
solar activity on modern Earth, and (2) the flare environment could
drive the atmosphere into a hydrodynamic loss regime at the observed
flare duty cycle: sustained exposure to the flare environment of GJ
699 results in the loss of ≍87 Earth atmospheres Gyr-1
through thermal processes and ≍3 Earth atmospheres Gyr-1
through ion loss processes. These results suggest that if rocky planet
atmospheres can survive the initial ∼5 Gyr of high stellar activity,
or if a second-generation atmosphere can be formed or acquired, the
flare duty cycle may be the controlling stellar parameter for the
stability of Earth-like atmospheres around old M stars.
Title: Modeling the Transport of Nonthermal Particles in Flares
Using Fokker-Planck Kinetic Theory
Authors: Allred, Joel C.; Alaoui, Meriem; Kowalski, Adam F.; Kerr,
Graham S.
Bibcode: 2020ApJ...902...16A
Altcode: 2020arXiv200810671A
We describe a new approach for modeling the transport of high-energy
particles accelerated during flares from the acceleration region
in the solar corona until their eventual thermalization in the
flare footpoint. Our technique numerically solves the Fokker-Planck
equation and includes forces corresponding to Coulomb collisions in a
flux loop with nonuniform ionization, synchrotron emission reaction,
magnetic mirroring, and a return current electric field. Our solution
to the Fokker-Planck equation includes second-order pitch angle and
momentum diffusion. It is applicable to particles of arbitrary mass
and charge. By tracking the collisions, we predict the bremsstrahlung
produced as these particles interact with the ambient stellar
atmosphere. This can be compared directly with observations and used
to constrain the accelerated particle energy distribution. We have
named our numerical code FP and distributed it for general use. We
demonstrate its effectiveness in several test cases.
Title: Solar Flare Energy Partitioning and Transport -- the Impulsive
Phase (a Heliophysics 2050 White Paper)
Authors: Kerr, Graham S.; Alaoui, Meriem; Allred, Joel C.; Bian,
Nicholas H.; Dennis, Brian R.; Emslie, A. Gordon; Fletcher, Lyndsay;
Guidoni, Silvina; Hayes, Laura A.; Holman, Gordon D.; Hudson, Hugh
S.; Karpen, Judith T.; Kowalski, Adam F.; Milligan, Ryan O.; Polito,
Vanessa; Qiu, Jiong; Ryan, Daniel F.
Bibcode: 2020arXiv200908400K
Altcode:
Solar flares are a fundamental component of solar eruptive events (SEEs;
along with solar energetic particles, SEPs, and coronal mass ejections,
CMEs). Flares are the first component of the SEE to impact our
atmosphere, which can set the stage for the arrival of the associated
SEPs and CME. Magnetic reconnection drives SEEs by restructuring the
solar coronal magnetic field, liberating a tremendous amount of energy
which is partitioned into various physical manifestations: particle
acceleration, mass and magnetic-field eruption, atmospheric heating,
and the subsequent emission of radiation as solar flares. To explain
and ultimately predict these geoeffective events, the heliophysics
community requires a comprehensive understanding of the processes that
transform and distribute stored magnetic energy into other forms,
including the broadband radiative enhancement that characterises
flares. This white paper, submitted to the Heliophysics 2050 Workshop,
discusses the flare impulsive phase part of SEEs, setting out the
questions that need addressing via a combination of theoretical,
modelling, and observational research. In short, by 2050 we must
determine the mechanisms of particle acceleration and propagation,
and must push beyond the paradigm of energy transport via nonthermal
electron beams, to also account for accelerated protons & ions
and downward directed Alfven waves.
Title: Solar Flare Energy Partitioning and Transport -- the Gradual
Phase (a Heliophysics 2050 White Paper)
Authors: Kerr, Graham S.; Alaoui, Meriem; Allred, Joel C.; Bian,
Nicholas H.; Dennis, Brian R.; Emslie, A. Gordon; Fletcher, Lyndsay;
Guidoni, Silvina; Hayes, Laura A.; Holman, Gordon D.; Hudson, Hugh
S.; Karpen, Judith T.; Kowalski, Adam F.; Milligan, Ryan O.; Polito,
Vanessa; Qiu, Jiong; Ryan, Daniel F.
Bibcode: 2020arXiv200908407K
Altcode:
Solar flares are a fundamental component of solar eruptive events
(SEEs; along with solar energetic particles, SEPs, and coronal
mass ejections, CMEs). Flares are the first component of the SEE
to impact our atmosphere, which can set the stage for the arrival
of the associated SEPs and CME. Magnetic reconnection drives SEEs
by restructuring the solar coronal magnetic field, liberating a
tremendous amount of energy which is partitioned into various physical
manifestations: particle acceleration, mass and magnetic-field eruption,
atmospheric heating, and the subsequent emission of radiation as solar
flares. To explain and ultimately predict these geoeffective events,
the heliophysics community requires a comprehensive understanding of
the processes that transform and distribute stored magnetic energy
into other forms, including the broadband radiative enhancement that
characterises flares. This white paper, submitted to the Heliophysics
2050 Workshop, discusses the flare gradual phase part of SEEs, setting
out the questions that need addressing via a combination of theoretical,
modelling, and observational research. In short, the flare gradual phase
persists much longer than predicted so, by 2050, we must identify the
characteristics of the significant energy deposition sustaining the
gradual phase, and address the fundamental processes of turbulence
and non-local heat flux.
Title: Optical and X-ray observations of stellar flares on an active
M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER
Authors: Namekata, Kosuke; Maehara, Hiroyuki; Sasaki, Ryo; Kawai,
Hiroki; Notsu, Yuta; Kowalski, Adam F.; Allred, Joel C.; Iwakiri,
Wataru; Tsuboi, Yohko; Murata, Katsuhiro L.; Niwano, Masafumi;
Shiraishi, Kazuki; Adachi, Ryo; Iida, Kota; Oeda, Motoki; Honda,
Satoshi; Tozuka, Miyako; Katoh, Noriyuki; Onozato, Hiroki; Okamoto,
Soshi; Isogai, Keisuke; Kimura, Mariko; Kojiguchi, Naoto; Wakamatsu,
Yasuyuki; Tampo, Yusuke; Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2020PASJ...72...68N
Altcode: 2020arXiv200504336N; 2020PASJ..tmp..218N
We report on multi-wavelength monitoring observations of an M-dwarf
flare star AD Leonis with the Seimei Telescope (6150-7930 Å), SCAT
(Spectroscopic Chuo-university Astronomical Telescope; 3700-7500 Å),
and NICER (Neutron Star Interior Composition Explorer; 0.2-12.0
keV), with the collaboration of the OISTER (Optical and Infrared
Synergetic Telescopes for Education and Research) program. Twelve
flares are detected in total, including ten Hα, four X-ray, and
four optical-continuum flares; one of them is a superflare with a
total energy of ∼2.0 × 1033 erg. We found that: (1)
during the superflare, the Hα emission line full width at 1/8 maximum
dramatically increases to 14 Å from 8 Å in the low-resolution spectra
(R ∼ 2000) accompanied by large white-light flares, (2) some weak
Hα/X-ray flares are not accompanied by white-light emissions, and (3)
the non-flaring emissions show clear rotational modulations in X-ray
and Hα intensity in the same phase. To understand these observational
features, one-dimensional hydrodynamic flare simulations are performed
using the RADYN code. We find the simulated Hα line profiles with
hard and high-energy non-thermal electron beams to be consistent with
the initial phase line profiles of the superflares, while those with
a softer and/or weak-energy beam are consistent with those in decay
phases, indicating the changes in the energy fluxes injected to the
lower atmosphere. Also, we find that the relation between the optical
continuum and Hα intensity is nonlinear, which can be one cause of the
non-white-light flares. The flare energy budget exhibits diversity in
the observations and models, and more observations of stellar flares
are necessary for constraining the occurrence of various emission line
phenomena in stellar flares.
Title: High-frequency Wave Power Observed in the Chromosphere with
IBIS and ALMA
Authors: Molnar, M. E.; Cranmer, S.; Reardon, K.; Kowalski, A.
Bibcode: 2020SPD....5120106M
Altcode:
The heating mechanism of the solar chromosphere is still an open
scientific question. In this work we study observational constraints on
the contribution to chromospheric heating from high-frequency acoustic
waves. We utilize a unique combination of observations from NSO's Dunn
Solar Telescope and from the Atacama Large Millimeter Array obtained
on April 23rd 2017 to estimate the high-frequency wave flux in the
lower solar atmosphere. The wave flux is inferred from comparison of
the observations with synthetic observables from the time-dependent
hydrodynamic RADYN code. Our findings suggest thatacoustic waves may
carry up to a few kW/m2 of flux, which is comparable to
what is required to heat the quiet chromosphere.
Title: Measuring Decay Timescales of Downflows in Solar Flare
Footpoints: Testing the One-minute Theory (Abstract)
Authors: Beltzer-Sweeney, A. K.; Butler, E.; Kowalski, A.; Cauzzi, G.
Bibcode: 2020JAVSO..48R.107B
Altcode:
(Abstract only) In 1989 George Fisher found analytically that
chromospheric downflows in flare footprints should slow down to
background detection levels within ~ 1 minute regardless of the initial
energy injected. We set to test this theory by measuring downflows in
flare kernels that were observed by the IRIS satellite between 2014
and 2017. The GOES classification system was used as a proxy for
the energy of the nonthermal electron beam that is thought to heat
the flare footprint. The redshift evolution of a Mg II triplet line
was measured in twenty-six C, M, and X class flares to determine the
timescale of deceleration of the chromospheric plasma in response to
explosive flare heating. Two different methods for measuring the decay
of the redshift as a function of time, bisector and gaussian, were
used to test the robustness of the inferred downflow gas velocities
across the wide variety of flares. Results of the analysis show
that downflow velocities reached 30 ~ 50 km/s, which is consistent
with previous results with a derived Mach number of 4 ~ 5. The times
of half-maximum velocity were found to be between 15 ~ 30 seconds,
indicating a rapid slowing. At later times, the Mg II line profiles
exhibit prolonged redshifts with inferred speeds of 5 to 7 km/s.
Title: Spectral Characteristics and Formation Height of Off-limb
Flare Ribbons
Authors: Kuridze, David; Mathioudakis, Mihalis; Heinzel, Petr; Koza,
Július; Morgan, Huw; Oliver, Ramon; Kowalski, Adam F.; Allred, Joel C.
Bibcode: 2020ApJ...896..120K
Altcode: 2020arXiv200510924K
Flare ribbons are bright manifestations of flare energy dissipation
in the lower solar atmosphere. For the first time, we report on
high-resolution imaging spectroscopy observations of flare ribbons
situated off limb in the Hβ and Ca II 8542 Å lines and make a detailed
comparison with radiative hydrodynamic simulations. Observations of
the X8.2 class solar flare SOL 2017-09-10T16:06 UT obtained with the
Swedish Solar Telescope reveal bright horizontal emission layers
in Hβ line-wing images located near the footpoints of the flare
loops. The apparent separation between the ribbon observed in the Hβ
wing and the nominal photospheric limb is about 300-500 km. The Ca II
8542 Å line-wing images show much fainter ribbon emissions located
right on the edge of the limb, without clear separation from the
limb. RADYN models are used to investigate synthetic spectral line
profiles for the flaring atmosphere, and good agreement is found
with the observations. The simulations show that, toward the limb,
where the line of sight is substantially oblique with respect to the
vertical direction, the flaring atmosphere model reproduces the high
contrast of the off-limb Hβ ribbons and their significant elevation
above the photosphere. The ribbons in the Ca II 8542 Å line-wing
images are located deeper in the lower solar atmosphere with a lower
contrast. A comparison of the height deposition of electron beam energy
and the intensity contribution function shows that the Hβ line-wing
intensities can be a useful tracer of flare energy deposition in the
lower solar atmosphere.
Title: Spectral Signatures of Chromospheric Condensation in a Major
Solar Flare
Authors: Graham, David R.; Cauzzi, Gianna; Zangrilli, Luca; Kowalski,
Adam; Simões, Paulo; Allred, Joel
Bibcode: 2020ApJ...895....6G
Altcode: 2020arXiv200405075G
We study the evolution of chromospheric line and continuum emission
during the impulsive phase of the X-class SOL2014-09-10T17:45
solar flare. We extend previous analyses of this flare to multiple
chromospheric lines of Fe I, Fe II, Mg II, C I, and Si II observed
with the Interface Region Imaging Spectrograph, combined with
radiative-hydrodynamical (RHD) modeling. For multiple flaring kernels,
the lines all show a rapidly evolving double-component structure: an
enhanced emission component at rest, and a broad, highly redshifted
component of comparable intensity. The redshifted components migrate
from 25 to 50 km s-1 toward the rest wavelength within ∼30
s. Using Fermi hard X-ray observations, we derive the parameters of
an accelerated electron beam impacting the dense chromosphere, using
them to drive an RHD simulation with the RADYN code. As in Kowalski
et al. (2017), our simulations show that the most energetic electrons
penetrate into the deep chromosphere, heating it to T ∼ 10,000 K,
while the bulk of the electrons dissipate their energy higher, driving
an explosive evaporation, and its counterpart condensation—a very
dense (ne ∼ 2 × 1014 cm-3), thin
layer (30-40 km thickness), heated to 8-12,000 K, moving toward the
stationary chromosphere at up to 50 km s-1. The synthetic
Fe II 2814.45 Å profiles closely resemble the observational
data, including a continuum enhancement, and both a stationary
and a highly redshifted component, rapidly moving toward the rest
wavelength. Importantly, the absolute continuum intensity, ratio
of component intensities, relative time of appearance, and redshift
amplitude are sensitive to the model input parameters, showing great
potential as diagnostics.
Title: Diagnosing a New Species of Dusty Debris: the Chameleon
Debris Disk
Authors: Wisniewski, John P.; Arnold, Jessica; Boccaletti, Anthony;
Debes, John Henry; Grady, Carol A.; Kowalski, Adam F.; Lomax, Jamie
R.; Sezestre, Elie; Weinberger, Alycia J.
Bibcode: 2020hst..prop16263W
Altcode:
Two new, potentially causally correlated, observational phenomena
have recently been discovered in spatially resolved imagery of debris
disks: outward moving features traveling at super-Keplerian velocities
and changes in the color of the AU Mic debris disk. To date, these
are the only moving structures and the only observed color change
seen in spatially resolved debris disks. We propose to use the only
observational facility capable of yielding high fidelity optical
coronagraphic spectroscopy of AU Mic's disk, HST/STIS, to obtain second
epoch G750L and first epoch G430L spectroscopy. These data will enable
us to: a) quantify color changes in the disk over a 2x greater time
baseline (16 yrs) than previously achieved; b) determine whether the
disk's color between 30-45 au continues to change as additional fast
moving features pass by; c) better quantify the size of dust grains
whose spatial distribution has changed; and d) confirm and better
quantify whether small grains populate small (10-30 au) stellocentric
distances. Derived grain size distributions will be linked to dynamical
models proposed for the origin of fast moving features in this system.
Title: Outflows and Disks around Young Stars: Synergies for the
Exploration of Ullyses Spectra (ODYSSEUS)
Authors: Herczeg, Gregory J.; Espaillat, Catherine; Abraham, Peter;
Alcala, Juan M.; Alencar, Silvia; Alexander, Richard; Antoniucci,
Simone; Ardila, David R.; Arulanantham, Nicole; Bacciotti, Francesca;
Beck, Tracy; Benisty, Myriam; Bergin, Edwin Anthony; Biazzo, Katia;
Bouvier, Jerome; Briceno, Cesar; Brown, Alexander; Cabrit, Sylvie;
Calvet, Nuria; Cleeves, Ilse; Coffey, Deirdre; Dougados, Catherine;
Edwards, Suzan; Eisloeffel, Jochen; Facchini, Stefano; Fedele, Davide;
Fischer, William J.; France, Kevin; Frasca, Antonio; Froebrich,
Dirk; Grankin, Konstantin; Guenther, Hans Moritz; Hartmann, Lee W.;
Hernandez, Jesus Omar; Hussain, Gaitee; Johns-Krull, Christopher
Michael; Kama, Mihkel; Kastner, Joel H.; Koen, Chris; Kospal, Agnes;
Kowalski, Adam F.; Manara, Carlo F.; Miotello, Anna; Muzerolle, James;
Nisini, Brunella; Panwar, Neelam; Principe, David; Robberto, Massimo;
Robinson, Connor; Schneider, Christian; Thanathibodee, Thanawuth;
Valenti, Jeff A.; Walter, Frederick M.; Williams, Jonathan P.; Xu,
Ziyan; Yadav, Ram Kesh
Bibcode: 2020hst..prop16129H
Altcode:
The ULLYSES DDT Survey of low-mass pre-main sequence stars, coupled
with forthcoming data from ALMA and JWST, will provide the foundation
to revolutionize our understanding of the relationship between young
stars and their protoplanetary disks. A comprehensive evaluation of the
physics of disk evolution and planet formation requires understanding
the intricate relationships between the mass accretion, mass outflow,
and disk structure. Our team of 55 young star experts from around
the world will bring their combined knowledge to bear on the ULLYSES
FUV spectral database, ensuring a uniform and systematic approach in
order to (1) measure how the accretion flow depends on the accretion
rate and magnetic structures, (2) determine where winds and jets
are launched and how mass loss rates compare to accretion, and (3)
establish the influence of FUV radiation on the chemistry of the warm
inner regions of planet-forming disks. We will also work together to
acquire and provide contemporaneous observations at X-ray, optical,
near-IR, and mm wavelengths to enhance the impact of the ULLYSES
data. By the end of our comprehensive 3-year program, we will provide
the best measurements of the levels and evolution of mass accretion
of protoplanetary disks, the properties and magnitudes of (inner)
disk mass loss, and the UV radiation fields that determine ionization
levels and drive disk chemistry. This team addresses the need for
labor essential to maximize the scientific return on the ULYSSES DDT
young star program, in line with funding requests allocated to Legacy
GO programs or Treasury programs.
Title: Neutron Production in M dwarf Flares
Authors: Kowalski, A. F.
Bibcode: 2020AAS...23517320K
Altcode:
M dwarfs are the most promising places for discovering Earth-mass
exoplanets in or near the traditional habitable zone. However, the
effects on habitability from M dwarf flares and their associated
(possible) coronal mass ejections are widely debated. An additional
factor that must be considered to evaluate the high-energy space weather
environment of M dwarfs is flare neutrons. High energy neutrons are
often detected during solar flares, but there are few that survive
to 1 au. We present the first calculations of neutron production and
propagation during M dwarf flares, and we estimate radiation doses on
the surfaces of hypothetical exoplanets. We discuss future prospects
with transit spectroscopy with the JWST and how flare neutrons provide
an unparalleled probe of particle acceleration and the heating in the
lower flaring stellar atmosphere.
Title: Blue asymmetries of Balmer lines during M-dwarf flares
investigated with multi-wavelength observations
Authors: Notsu, Y.; Kowalski, A.; Maehara, H.; Namekata, K.; Hawley,
S.; Davenport, J.; Enoto, T.; Hamaguchi, K.; Honda, S.; Notsu, S.;
Ikuta, K.; Nogami, D.; Shibata, K.
Bibcode: 2020AAS...23528805N
Altcode:
Flares are magnetic energy release in the solar/stellar atmosphere,
and they have strong emissions from radio to X-rays. During some
M-dwarf superflares, chromospheric line profiles show blue asymmetries
(Honda et al. 2018), though red asymmetries have been seen during many
ordinary solar flares. it is also thought that similar enhancements of
the blue wing of Balmer lines can provide clues for investigating mass
ejections from flares (stellar CMEs) (cf. Vida et al. 2016&2019),
but this is still very controversial. Thus, we need more flare
spectroscopic observations with high time resolution for understanding
how superflares occur and how large mass ejections occur during
superflares occur. The latter is helpful for estimating the impacts
on planets from superflares. We have conducted several simultaneous
spectroscopic and photometric observations of M-dwarf flare stars. In
2019 January, we observed a M-dwarf flare star YZCMi using APO3.5m/ARCES
(high-dispersion spectroscopy), APO/ARCSAT0.5m (multi-color photometry),
TESS (space high-precision single-color photometry), and NICER (soft
X-ray telescope on ISS). During the observation, we detected large
enhancements of chromospheric lines lasting for longer than 3 hours
(e.g., H- alpha and H-beta). H-alpha line profiles during this event
show some blue asymmetries. In this event, we also detected soft
X-ray intensity increases, but a bit strangely and a bit different
from previous expectations, the photometric data (optical continuum
white light data) show no clear flare-like brightness increases. This
might suggest that these intensity increases of chromospheric lines
(with possible blue asymmetries) and soft X-rays occurred as a
"non white-light" flare events, which are often seen in the case of
solar flares (e.g., Watanabe et al. 2017). We also observed another
M-dwarf flare star AU Mic using CTIO/SMART1.5m/CHIRON (high-dispersion
spectroscopy), LCO (U&V-band photometry), and XMM-Newton (soft
X-ray), and detected several flares in Oct 2018. In contrast to the
above "non-white light" events, these flares show enhancements in
Balmer lines (e.g., H-alpha), optical continuum white light, and soft
X-ray. Then this event is a so-called "white-light" flare. Moreover,
this "white-light" event does not show clear blue asymmetries, which are
different from the above YZCMi "non-white light" event. In this poster,
we introduce ongoing results on the analyses of these two events.
Title: Coronal dimming as a proxy for stellar coronal mass ejections
Authors: Jin, M.; Cheung, M. C. M.; DeRosa, M. L.; Nitta, N. V.;
Schrijver, C. J.; France, K.; Kowalski, A.; Mason, J. P.; Osten, R.
Bibcode: 2020IAUS..354..426J
Altcode: 2020arXiv200206249J
Solar coronal dimmings have been observed extensively in the past
two decades and are believed to have close association with coronal
mass ejections (CMEs). Recent study found that coronal dimming
is the only signature that could differentiate powerful flares
that have CMEs from those that do not. Therefore, dimming might be
one of the best candidates to observe the stellar CMEs on distant
Sun-like stars. In this study, we investigate the possibility of using
coronal dimming as a proxy to diagnose stellar CMEs. By simulating a
realistic solar CME event and corresponding coronal dimming using a
global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model),
we first demonstrate the capability of the model to reproduce solar
observations. We then extend the model for simulating stellar CMEs
by modifying the input magnetic flux density as well as the initial
magnetic energy of the CME flux rope. Our result suggests that with
improved instrument sensitivity, it is possible to detect the coronal
dimming signals induced by the stellar CMEs.
Title: Measuring Decay Timescales of Downflows in Solar Flare
Footpoints: Testing the 1-minute Theory
Authors: Beltzer-Sweeney, A. K.; Butler, E.; Kowalski, A. F.;
Cauzzi, G.
Bibcode: 2019AGUFMSH13D3423B
Altcode:
In 1989 George Fisher found analytically that chromospheric downflows in
flare footprints should slow down to background detection levels within
~1 minute regardless of the initial energy injected. We set to test
this theory by measuring downflows in flare kernels that were observed
by the IRIS satellite between 2014-2017. The GOES classification system
was used as a proxy for the energy of the nonthermal electron beam
that is thought to heat the flare footprint. The redshift evolution
of a Mg II triplet line was measured in twenty-six C, M, and X class
flares to determine the timescale of deceleration of the chromospheric
plasma in response to explosive flare heating. Two different methods
for measuring the decay of the redshift as a function of time, bisector
and gaussian, were used to test the robustness of the inferred downflow
gas velocities across the wide variety of flares. Results of the
analysis show that downflow velocities reached 30~50 km/s, which is
consistent with previous results with a derived Mach number of 4~5. The
times of half-maximum velocity were found to be between 15~30 seconds,
indicating a rapid slowing. At later times, the Mg II line profiles
exhibit prolonged redshifts with inferred speeds of 5-7 km/s.
Title: Identification of Stellar Flares Using Differential Evolution
Template Optimization
Authors: Lawson, Kellen D.; Wisniewski, John P.; Bellm, Eric C.;
Kowalski, Adam F.; Shupe, David L.
Bibcode: 2019AJ....158..119L
Altcode: 2019arXiv190303240L
We explore methods for the identification of stellar flare events
in irregularly sampled data of ground-based time domain surveys. In
particular, we describe a new technique for identifying flaring stars,
which we have implemented in a publicly available Python module called
“PyVAN.” The approach uses the Differential Evolution algorithm to
optimize parameters of empirically derived light curve templates for
different types of stars to fit a candidate light curve. The difference
of the likelihoods that these best-fit templates produced the observed
data is then used to delineate targets that are well-explained by a
flare template but simultaneously poorly explained by templates of
common contaminants. By testing on light curves of known identity
and morphology, we show that our technique is capable of recovering
flaring status in 69% of all light curves containing a flare event above
thresholds drawn to include <1% of any contaminant population. By
applying to Palomar Transient Factory data, we show consistency with
prior samples of flaring stars, and identify a small selection of
candidate flaring G-type stars for possible follow-up.
Title: STROBE-X: X-ray Timing and Spectroscopy on Dynamical Timescales
from Microseconds to Years
Authors: Ray, Paul; Arzoumanian, Zaven; Ballantyne, David; Bozzo,
Enrico; Brandt, Soren; Brenneman, Laura; Chakrabarty, Deepto;
Christophersen, Marc; DeRosa, Alessandra; Feroci, Marco; Gendreau,
Keith; Goldstein, Adam; Hartmann, Dieter; Hernanz, Margarita; Jenke,
Peter; Kara, Erin; Maccarone, Tom; McDonald, Michael; Martindale,
Adrian; Nowak, Michael; Phlips, Bernard; Remillard, Ron; Schanne,
Stephane; Stevens, Abigail; Tomsick, John; Watts, Anna; Wilson-Hodge,
Colleen; Wolff, Michael; Wood, Kent; Zane, Silvia; Ajello, Marco;
Alston, Will; Altamirano, Diego; Antoniou, Vallia; Arur, Kavitha;
Ashton, Dominic; Auchettl, Katie; Ayres, Tom; Bachetti, Matteo;
Balokovic, Mislav; Baring, Matthew; Baykal, Altan; Begelman, Mitch;
Bhat, Narayana; Bogdanov, Slavko; Briggs, Michael; Bulbul, Esra;
Bult, Petrus; Burns, Eric; Cackett, Ed; Campana, Riccardo; Caspi,
Amir; Cavecchi, Yuri; Chenevez, Jerome; Cherry, Mike; Corbet, Robin;
Corcoran, Michael; Corsi, Alessandra; Degenaar, Nathalie; Drake,
Jeremy; Eikenberry, Steve; Enoto, Teruaki; Fragile, Chris; Fuerst,
Felix; Gandhi, Poshak; Garcia, Javier; Goldstein, Adam; Gonzalez,
Anthony; Grefenstette, Brian; Grinberg, Victoria; Grossan, Bruce;
Guillot, Sebastien; Guver, Tolga; Haggard, Daryl; Heinke, Craig;
Heinz, Sebastian; Hemphill, Paul; Homan, Jeroen; Hui, Michelle;
Huppenkothen, Daniela; Ingram, Adam; Irwin, Jimmy; Jaisawal, Gaurava;
Jaodand, Amruta; Kalemci, Emrah; Kaplan, David; Keek, Laurens; Kennea,
Jamie; Kerr, Matthew; van der Klis, Michiel; Kocevski, Daniel; Koss,
Mike; Kowalski, Adam; Lai, Dong; Lamb, Fred; Laycock, Silas; Lazio,
Joseph; Lazzati, Davide; Longcope, Dana; Loewenstein, Michael; Maitra,
Dipankair; Majid, Walid; Maksym, W. Peter; Malacaria, Christian;
Margutti, Raffaella; Martindale, Adrian; McHardy, Ian; Meyer, Manuel;
Middleton, Matt; Miller, Jon; Miller, Cole; Motta, Sara; Neilsen, Joey;
Nelson, Tommy; Noble, Scott; O'Brien, Paul; Osborne, Julian; Osten,
Rachel; Ozel, Feryal; Palliyaguru, Nipuni; Pasham, Dheeraj; Patruno,
Alessandro; Pelassa, Vero; Petropoulou, Maria; Pilia, Maura; Pohl,
Martin; Pooley, David; Prescod-Weinstein, Chanda; Psaltis, Dimitrios;
Raaijmakers, Geert; Reynolds, Chris; Riley, Thomas E.; Salvesen, Greg;
Santangelo, Andrea; Scaringi, Simone; Schanne, Stephane; Schnittman,
Jeremy; Smith, David; Smith, Krista Lynne; Snios, Bradford; Steiner,
Andrew; Steiner, Jack; Stella, Luigi; Strohmayer, Tod; Sun, Ming;
Tauris, Thomas; Taylor, Corbin; Tohuvavohu, Aaron; Vacchi, Andrea;
Vasilopoulos, Georgios; Veledina, Alexandra; Walsh, Jonelle; Weinberg,
Nevin; Wilkins, Dan; Willingale, Richard; Wilms, Joern; Winter,
Lisa; Wolff, Michael; in 't Zand, Jean; Zezas, Andreas; Zhang, Bing;
Zoghbi, Abdu
Bibcode: 2019BAAS...51g.231R
Altcode: 2019astro2020U.231R
STROBE-X is a probe-class mission concept, selected for study by NASA,
for X-ray spectral timing of compact objects across the mass scale. It
combines huge collecting area, high throughput, broad energy coverage,
and excellent spectral and temporal resolution in a single facility,
enabling a broad portfolio of high-priority astrophysics.
Title: High-fidelity Imaging of the Inner AU Mic Debris Disk:
Evidence of Differential Wind Sculpting?
Authors: Wisniewski, John P.; Kowalski, Adam F.; Davenport, James
R. A.; Schneider, Glenn; Grady, Carol A.; Hebb, Leslie; Lawson, Kellen
D.; Augereau, Jean-Charles; Boccaletti, Anthony; Brown, Alexander;
Debes, John H.; Gaspar, Andras; Henning, Thomas K.; Hines, Dean C.;
Kuchner, Marc J.; Lagrange, Anne-Marie; Milli, Julien; Sezestre,
Elie; Stark, Christopher C.; Thalmann, Christian
Bibcode: 2019ApJ...883L...8W
Altcode: 2019arXiv190710113W
We present new high-fidelity optical coronagraphic imagery of the inner
∼50 au of AU Mic’s edge-on debris disk using the BAR5 occulter of
the Hubble Space Telescope Imaging Spectrograph (HST/STIS) obtained on
2018 July 26-27. This new imagery reveals that “feature A,” residing
at a projected stellocentric separation of 14.2 au on the southeast side
of the disk, exhibits an apparent “loop-like” morphology at the time
of our observations. The loop has a projected width of 1.5 au and rises
2.3 au above the disk midplane. We also explored Transiting Exoplanet
Survey Satellite photometric observations of AU Mic that are consistent
with evidence of two starspot complexes in the system. The likely
co-alignment of the stellar and disk rotational axes breaks degeneracies
in detailed spot modeling, indicating that AU Mic’s projected magnetic
field axis is offset from its rotational axis. We speculate that small
grains in AU Mic’s disk could be sculpted by a time-dependent wind
that is influenced by this offset magnetic field axis, analogous to
co-rotating solar interaction regions that sculpt and influence the
inner and outer regions of our own Heliosphere. Alternatively, if the
observed spot modulation is indicative of a significant misalignment
of the stellar and disk rotational axes, we suggest that the disk
could still be sculpted by the differential equatorial versus polar
wind that it sees with every stellar rotation.
Title: Measurements of the Ultraviolet Spectral Characteristics of
Low-mass Exoplanetary Systems (Mega-MUSCLES)
Authors: Wilson, David John; Froning, Cynthia; France, Kevin;
Youngblood, Allison; Duvvuri, Girish M.; Brown, Alexander; Schneider,
P. Christian; Kowalski, Adam; Loyd, R. O. Parke; Berta-Thompson,
Zachory Berta-; Pineda, J. Sebastian; Linsky, Jeffrey; Rugheimer,
Sarah; Newton, Elizabeth; Miguel, Yamila; Roberge, Aki; Buccino,
Andrea P.; Irwin, Jonathan; Kaltenegger, Lisa; Vieytes, Mariela;
Mauas, Pablo; Redfield, Seth; Hawley, Suzanne; Tian, Feng
Bibcode: 2019ESS.....431906W
Altcode:
M dwarf stars have emerged as ideal targets for exoplanet
observations. Their small radii aids planetary discovery, their
close-in habitable zones allow short observing campaigns, and their
red spectra provide opportunities for transit spectroscopy with
JWST. The potential of M dwarfs has been underlined by the discovery
of remarkable systems such as the seven Earth-sized planets orbiting
TRAPPIST-1 and the habitable-zone planet around the closest star to
the Sun. However, to accurately assess the conditions in these
systems requires a firm understanding of how M dwarfs differ from the
Sun, beyond just their smaller size and mass. Of particular importance
are the time-variable, high-energy ultraviolet and x-ray regions of
the M dwarf spectral energy distribution (SED), which can influence
the chemistry and lifetime of exoplanet atmospheres, as well as their
surface radiation environments. The Measurements of the Ultraviolet
Spectral Characteristics of Low-mass Exoplanetary Systems (Mega-MUSCLES)
Treasury project, together with the precursor MUSCLES project, aims to
produce full SEDs of a representative sample of M dwarfs, covering a
wide range of stellar mass, age, and planetary system architecture. We
have obtained x-ray and ultraviolet data for 13 stars using the Hubble,
Chandra and XMM space telescopes, along with ground-based data in the
optical and state-of-the-art DEM modelling to fill in the unobservable
extreme ultraviolet regions. Our completed SEDs will be available as a
community resource, with the aim that a close MUSCLES analogue should
exist for most M dwarfs of interest. In this presentation I will
overview the Mega-MUSCLES project, describing our choice of targets,
observation strategy and SED production methodology. I will also
discuss notable targets such as the TRAPPIST-1 host star, comparing
our observations with previous data and model predictions. Finally,
I will present an exciting by-product of the Mega-MUSCLES project:
time-resolved ultraviolet spectroscopy of stellar flares at multiple
targets, spanning a range of stellar types, ages and flare energies.
Title: Modeling Mg II h, k and Triplet Lines at Solar Flare Ribbons
Authors: Zhu, Yingjie; Kowalski, Adam F.; Tian, Hui; Uitenbroek, Han;
Carlsson, Mats; Allred, Joel C.
Bibcode: 2019ApJ...879...19Z
Altcode: 2019arXiv190412285Z
Observations from the Interface Region Imaging Spectrograph often
reveal significantly broadened and non-reversed profiles of the Mg II
h, k and triplet lines at flare ribbons. To understand the formation
of these optically thick Mg II lines, we perform plane-parallel
radiative hydrodynamics modeling with the RADYN code, and then
recalculate the Mg II line profiles from RADYN atmosphere snapshots
using the radiative transfer code RH. We find that the current RH
code significantly underestimates the Mg II h and k Stark widths. By
implementing semiclassical perturbation approximation results of
quadratic Stark broadening from the STARK-B database in the RH code,
the Stark broadenings are found to be one order of magnitude larger
than those calculated from the current RH code. However, the improved
Stark widths are still too small, and another factor of 30 has to be
multiplied to reproduce the significantly broadened lines and adjacent
continuum seen in observations. Nonthermal electrons, magnetic fields,
three-dimensional effects, or electron density effects may account
for this factor. Without modifying the RADYN atmosphere, we have also
reproduced non-reversed Mg II h and k profiles, which appear when the
electron beam energy flux is decreasing. These profiles are formed at
an electron density of ∼8 × 1014 cm-3 and a
temperature of ∼1.4 × 104 K, where the source function
slightly deviates from the Planck function. Our investigation also
demonstrates that at flare ribbons the triplet lines are formed in the
upper chromosphere, close to the formation heights of the h and k lines.
Title: The Focusing Optics X-ray Solar Imager (FOXSI)
Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener,
Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Gburek, Szymon;
Steslicki, Marek; Allred, Joel C.; Battaglia, Marina; Baumgartner,
Wayne H.; Drake, James; Goetz, Keith; Grefenstette, Brian; Hannah,
Iain; Holman, Gordon D.; Inglis, Andrew; Ireland, Jack; Klimchuk,
James A.; Ishikawa, Shin-Nosuke; Kontar, Eduard; Massone, Anna-maria;
Piana, Michele; Ramsey, Brian; Schwartz, Richard A.; Woods, Thomas N.;
Chen, Bin; Gary, Dale E.; Hudson, Hugh S.; Kowalski, Adam; Warmuth,
Alexander; White, Stephen M.; Veronig, Astrid; Vilmer, Nicole
Bibcode: 2019AAS...23422501C
Altcode:
The Focusing Optics X-ray Solar Imager (FOXSI), a SMEX mission concept
in Phase A, is the first-ever solar-dedicated, direct-imaging, hard
X-ray telescope. FOXSI provides a revolutionary new approach to
viewing explosive magnetic-energy release on the Sun by detecting
signatures of accelerated electrons and hot plasma directly in
and near the energy-release sites of solar eruptive events (e.g.,
solar flares). FOXSI's primary science objective is to understand the
mystery of how impulsive energy release leads to solar eruptions, the
primary drivers of space weather at Earth, and how those eruptions are
energized and evolve. FOXSI addresses three important science questions:
(1) How are particles accelerated at the Sun? (2) How do solar plasmas
get heated to high temperatures? (3) How does magnetic energy released
on the Sun lead to flares and eruptions? These fundamental physics
questions are key to our understanding of phenomena throughout
the Universe from planetary magnetospheres to black hole accretion
disks. FOXSI measures the energy distributions and spatial structure of
accelerated electrons throughout solar eruptive events for the first
time by directly focusing hard X-rays from the Sun. This naturally
enables high imaging dynamic range, while previous instruments have
typically been blinded by bright emission. FOXSI provides 20-100 times
more sensitivity as well as 20 times faster imaging spectroscopy
than previously available, probing physically relevant timescales
(<1 second) never before accessible. FOXSI's launch in July 2022
is aligned with the peak of the 11-year solar cycle, enabling FOXSI
to observe the many large solar eruptions that are expected to take
place throughout its two-year mission.
Title: Spectral Evidence for Heating at Large Column Mass in Umbral
Solar Flare Kernels. I. IRIS Near-UV Spectra of the X1 Solar Flare
of 2014 October 25
Authors: Kowalski, Adam F.; Butler, Elizabeth; Daw, Adrian N.;
Fletcher, Lyndsay; Allred, Joel C.; De Pontieu, Bart; Kerr, Graham S.;
Cauzzi, Gianna
Bibcode: 2019ApJ...878..135K
Altcode: 2019arXiv190502111K
The GOES X1 flare SOL2014-10-25T17:08:00 was a three-ribbon solar
flare observed with the Interface Region Imaging Spectrograph (IRIS)
in the near-UV (NUV) and far-UV. One of the flare ribbons crossed
a sunspot umbra, producing a dramatic, ∼1000% increase in the NUV
continuum radiation. We comprehensively analyze the UV spectral data
of the umbral flare brightenings, which provide new challenges for
radiative-hydrodynamic modeling of the chromospheric velocity field and
the white-light continuum radiation. The emission line profiles in the
umbral flare brightenings exhibit redshifts and profile asymmetries,
but these are significantly smaller than in another, well-studied
X-class solar flare. We present a ratio of the NUV continuum intensity
to the Fe II λ2814.45 intensity. This continuum-to-line ratio is a
new spectral diagnostic of significant heating at high column mass
(log m/[g cm-2] > -2) during solar flares because the
continuum and emission line radiation originate from relatively similar
temperatures but moderately different optical depths. The full spectral
readout of these IRIS data also allow for a comprehensive survey of the
flaring NUV landscape: in addition to many lines of Fe II and Cr II, we
identify a new solar flare emission line, He I λ2829.91 (as previously
identified in laboratory and early-type stellar spectra). The Fermi/GBM
hard X-ray data provide inputs to radiative-hydrodynamic models (which
will be presented in Paper II) in order to better understand the large
continuum-to-line ratios, the origin of the white-light continuum
radiation, and the role of electron beam heating in the low atmosphere.
Title: High Resolution Observations of Chromospheric Condensation
Authors: Cauzzi, Gianna; Graham, David; Zangrilli, Luca; Kowalski, Adam
Bibcode: 2019shin.confE.180C
Altcode:
The chromospheric response to flaring can provide information on
the coronal magnetic reconnection processes driving the flare. In
particular, the evolution of the chromospheric condensation can
trace the site and size of episodes of energy release in the corona,
and inform on their duration. High resolution, spectrally resolved
observations of chromospheric lines and continua are necessary to fully
study this phenomenon. High cadence observations of chromospheric
condensation in small flaring kernels, derived from a multi-spectral
analysis of IRIS UV lines in a well-studied X1 flare, put some hard
constraints on these values. In particular, it is found that the
chromospheric signatures occurr sequentially in multiple distinct
positions, separated by only 0.3"
Title: EUV observations of cool dwarf stars
Authors: Youngblood, Allison; Drake, Jeremy; Mason, James; Osten,
Rachel; Jin, Meng; Kowalski, Adam; France, Kevin; Fleming, Brian;
Allred, Joel; Amerstorfer, Ute; Berta-Thompson, Zachory; Bourrier,
Vincent; Fossati, Luca; Froning, Cynthia; Garraffo, Cecilia; Gronoff,
Guillaume; Koskinen, Tommi; Lichtenegger, Herbert
Bibcode: 2019BAAS...51c.300Y
Altcode: 2019astro2020T.300Y; 2019arXiv190305719Y
The EUV (100-912 Å) probes regions of the stellar atmosphere that
are inaccessible from other spectral regions, including cool coronal
emission lines that offer the clearest path toward detecting coronal
mass ejections on stars other than the Sun. New EUV observations would
require a dedicated grazing-incidence observatory.
Title: EUV influences on exoplanet atmospheric stability and evolution
Authors: Youngblood, Allison; France, Kevin; Koskinen, Tommi; Fossati,
Luca; Amerstorfer, Ute; Lichtenegger, Herbert; Drake, Jeremy; Mason,
James; Fleming, Brian; Allred, Joel; Berta-Thompson, Zachory; Bourrier,
Vincent; Froning, Cynthia; Garraffo, Cecilia; Gronoff, Guillaume;
Jin, Meng; Kowalski, Adam; Osten, Rachel
Bibcode: 2019BAAS...51c.320Y
Altcode: 2019astro2020T.320Y; 2019arXiv190305718Y
EUV photons (100-912 Å) drive atmospheric mass loss, and an accurate
accounting of the EUV in a planet's energy budget is essential. Direct
EUV observations of exoplanet host stars would require a new, dedicated
observatory. Archival observations from EUVE and models are insufficient
to accurately characterize EUV spectra of exoplanet host stars.
Title: Developing a vision for exoplanetary transit spectroscopy:
a shared window on the analysis of planetary atmospheres and of
stellar magnetic structure
Authors: Kowalski, Adam; Schrijver, Karel; Pillet, Valentin; Criscuoli,
Serena
Bibcode: 2019BAAS...51c.149K
Altcode: 2019astro2020T.149K; 2019arXiv190405976K
We describe how accurate exoplanet atmospheres' characterization will
inevitably require taking into consideration stellar inhomogeneities
caused by convection and magnetic fields. Disentangling these two
components requires a multipronged approach with new solar reference
spectra, MHD modeling, and collaborations among astrophysics
communities.
Title: STROBE-X: X-ray Timing and Spectroscopy on Dynamical Timescales
from Microseconds to Years
Authors: Ray, Paul S.; Arzoumanian, Zaven; Ballantyne, David;
Bozzo, Enrico; Brandt, Soren; Brenneman, Laura; Chakrabarty, Deepto;
Christophersen, Marc; DeRosa, Alessandra; Feroci, Marco; Gendreau,
Keith; Goldstein, Adam; Hartmann, Dieter; Hernanz, Margarita;
Jenke, Peter; Kara, Erin; Maccarone, Tom; McDonald, Michael;
Nowak, Michael; Phlips, Bernard; Remillard, Ron; Stevens, Abigail;
Tomsick, John; Watts, Anna; Wilson-Hodge, Colleen; Wood, Kent; Zane,
Silvia; Ajello, Marco; Alston, Will; Altamirano, Diego; Antoniou,
Vallia; Arur, Kavitha; Ashton, Dominic; Auchettl, Katie; Ayres, Tom;
Bachetti, Matteo; Balokovic, Mislav; Baring, Matthew; Baykal, Altan;
Begelman, Mitch; Bhat, Narayana; Bogdanov, Slavko; Briggs, Michael;
Bulbul, Esra; Bult, Petrus; Burns, Eric; Cackett, Ed; Campana,
Riccardo; Caspi, Amir; Cavecchi, Yuri; Chenevez, Jerome; Cherry,
Mike; Corbet, Robin; Corcoran, Michael; Corsi, Alessandra; Degenaar,
Nathalie; Drake, Jeremy; Eikenberry, Steve; Enoto, Teruaki; Fragile,
Chris; Fuerst, Felix; Gandhi, Poshak; Garcia, Javier; Goldstein,
Adam; Gonzalez, Anthony; Grefenstette, Brian; Grinberg, Victoria;
Grossan, Bruce; Guillot, Sebastien; Guver, Tolga; Haggard, Daryl;
Heinke, Craig; Heinz, Sebastian; Hemphill, Paul; Homan, Jeroen;
Hui, Michelle; Huppenkothen, Daniela; Ingram, Adam; Irwin, Jimmy;
Jaisawal, Gaurava; Jaodand, Amruta; Kalemci, Emrah; Kaplan, David;
Keek, Laurens; Kennea, Jamie; Kerr, Matthew; van der Klis, Michiel;
Kocevski, Daniel; Koss, Mike; Kowalski, Adam; Lai, Dong; Lamb, Fred;
Laycock, Silas; Lazio, Joseph; Lazzati, Davide; Longcope, Dana;
Loewenstein, Michael; Maitra, Dipankair; Majid, Walid; Maksym,
W. Peter; Malacaria, Christian; Margutti, Raffaella; Martindale,
Adrian; McHardy, Ian; Meyer, Manuel; Middleton, Matt; Miller, Jon;
Miller, Cole; Motta, Sara; Neilsen, Joey; Nelson, Tommy; Noble,
Scott; O'Brien, Paul; Osborne, Julian; Osten, Rachel; Ozel, Feryal;
Palliyaguru, Nipuni; Pasham, Dheeraj; Patruno, Alessandro; Pelassa,
Vero; Petropoulou, Maria; Pilia, Maura; Pohl, Martin; Pooley, David;
Prescod-Weinstein, Chanda; Psaltis, Dimitrios; Raaijmakers, Geert;
Reynolds, Chris; Riley, Thomas E.; Salvesen, Greg; Santangelo, Andrea;
Scaringi, Simone; Schanne, Stephane; Schnittman, Jeremy; Smith, David;
Smith, Krista Lynne; Snios, Bradford; Steiner, Andrew; Steiner, Jack;
Stella, Luigi; Strohmayer, Tod; Sun, Ming; Tauris, Thomas; Taylor,
Corbin; Tohuvavohu, Aaron; Vacchi, Andrea; Vasilopoulos, Georgios;
Veledina, Alexandra; Walsh, Jonelle; Weinberg, Nevin; Wilkins, Dan;
Willingale, Richard; Wilms, Joern; Winter, Lisa; Wolff, Michael; in
't Zand, Jean; Zezas, Andreas; Zhang, Bing; Zoghbi, Abdu
Bibcode: 2019arXiv190303035R
Altcode:
We present the Spectroscopic Time-Resolving Observatory for Broadband
Energy X-rays (STROBE-X), a probe-class mission concept selected for
study by NASA. It combines huge collecting area, high throughput, broad
energy coverage, and excellent spectral and temporal resolution in a
single facility. STROBE-X offers an enormous increase in sensitivity
for X-ray spectral timing, extending these techniques to extragalactic
targets for the first time. It is also an agile mission capable of
rapid response to transient events, making it an essential X-ray
partner facility in the era of time-domain, multi-wavelength, and
multi-messenger astronomy. Optimized for study of the most extreme
conditions found in the Universe, its key science objectives include:
(1) Robustly measuring mass and spin and mapping inner accretion
flows across the black hole mass spectrum, from compact stars to
intermediate-mass objects to active galactic nuclei. (2) Mapping out
the full mass-radius relation of neutron stars using an ensemble of
nearly two dozen rotation-powered pulsars and accreting neutron stars,
and hence measuring the equation of state for ultradense matter
over a much wider range of densities than explored by NICER. (3)
Identifying and studying X-ray counterparts (in the post-Swift era)
for multiwavelength and multi-messenger transients in the dynamic sky
through cross-correlation with gravitational wave interferometers,
neutrino observatories, and high-cadence time-domain surveys in other
electromagnetic bands. (4) Continuously surveying the dynamic X-ray
sky with a large duty cycle and high time resolution to characterize
the behavior of X-ray sources over an unprecedentedly vast range of
time scales. STROBE-X's formidable capabilities will also enable a
broad portfolio of additional science.
Title: A Hot Ultraviolet Flare on the M Dwarf Star GJ 674
Authors: Froning, Cynthia S.; Kowalski, Adam; France, Kevin; Loyd,
R. O. Parke; Schneider, P. Christian; Youngblood, Allison; Wilson,
David; Brown, Alexander; Berta-Thompson, Zachory; Pineda, J. Sebastian;
Linsky, Jeffrey; Rugheimer, Sarah; Miguel, Yamila
Bibcode: 2019ApJ...871L..26F
Altcode:
As part of the Mega-Measurements of the Ultraviolet Spectral
Characteristics of Low-Mass Exoplanetary Systems Hubble Space Telescope
(HST) Treasury program, we obtained time-series ultraviolet spectroscopy
of the M2.5V star, GJ 674. During the far-ultraviolet (FUV) monitoring
observations, the target exhibited several small flares and one large
flare (E FUV = 1030.75 erg) that persisted
over the entirety of an HST orbit and had an equivalent duration
>30,000 s, comparable to the highest relative amplitude event
previously recorded in the FUV. The flare spectrum exhibited enhanced
line emission from chromospheric, transition region, and coronal
transitions and a blue FUV continuum with an unprecedented color
temperature of TC ≃ 40,000 ± 10,000 K. In this Letter,
we compare the flare FUV continuum emission with parameterizations of
radiative hydrodynamic model atmospheres of M star flares. We find that
the observed flare continuum can be reproduced using flare models but
only with the ad hoc addition of a hot, dense emitting component. This
observation demonstrates that flares with hot FUV continuum temperatures
and significant extreme-ultraviolet/FUV energy deposition will continue
to be of importance to exoplanet atmospheric chemistry and heating, even
as the host M dwarfs age beyond their most active evolutionary phases.
Title: The Near-ultraviolet Continuum Radiation in the Impulsive
Phase of HF/GF-type dMe Flares. I. Data
Authors: Kowalski, Adam F.; Wisniewski, John P.; Hawley, Suzanne L.;
Osten, Rachel A.; Brown, Alexander; Fariña, Cecilia; Valenti, Jeff
A.; Brown, Stephen; Xilouris, Manolis; Schmidt, Sarah J.; Johns-Krull,
Christopher
Bibcode: 2019ApJ...871..167K
Altcode: 2018arXiv181104021K
We present near-UV (NUV) flare spectra from the Hubble Space Telescope
(HST)/Cosmic Origins Spectrograph during two moderate-amplitude
U-band flares on the dM4e star GJ 1243. These spectra are some of
the first accurately flux-calibrated, NUV flare spectra obtained
over the impulsive phase in M dwarf flares. We observed these flares
with a fleet of nine ground-based telescopes simultaneously, which
provided broadband photometry and low-resolution spectra at the
Balmer jump. An increase in the broadband continuum occurred with a
signal-to-noise ratio >20 in the HST spectra, while numerous Fe
II lines and the Mg II lines also increased but with smaller flux
enhancements than the continuum radiation. These two events produced
the most prominent Balmer line radiation and the largest Balmer jumps
that have been observed to date in dMe flare spectra. A T = 9000 K
blackbody underestimates the NUV continuum flare flux by a factor of
two and is a poor approximation to the white light in these types of
flare events. Instead, our data suggest that the peak of the specific
continuum flux density is constrained to U-band wavelengths near the
Balmer series limit. A radiative-hydrodynamic simulation of a very
high energy deposition rate averaged over times of impulsive heating
and cooling better explains the properties of the λ > 2500 Å
flare continuum. These two events sample only one end of the empirical
color-color distribution for dMe flares, and more time-resolved flare
spectra in the NUV, U band, and optical from 2000 to 4200 Å are needed
during more impulsive and/or more energetic flares.
Title: Ultraviolet Properties of a Large Flare on GJ 674
Authors: Froning, Cynthia S.; Kowalski, Adam; France, Kevin; Loyd,
R. P.; Youngblood, Allison; Schneider, Christian; Wilson, David;
Rugheimer, Sarah
Bibcode: 2019AAS...23311401F
Altcode:
As part of the Mega-MUSCLES HST Treasury Program, our team observed the
exoplanet host star, GJ 674, in April of 2018. During seven orbits of
HST ultraviolet spectroscopic observations with COS and STIS, GJ 674
exhibited several small flares and two large ones, the most energetic
of which persisted over the entire COS orbit and has an integrated
FUV (1070-1360A) flux of 10^30.8 erg. The flare spectrum exhibits
line emission from tracers of the stellar chromosphere (CII, CIII,
SiII, SiIII, SiIV, NV) and corona (Fe XII, FE XIX, Fe XXI). The flare
spectrum is also distinguished by strong, blue continuum emission
which can be fit by a blackbody with a brightness temperature of
Tbr = 40,000+/-10,000 K. In this presentation, we compare the flare
UV properties to parameterizations of RHD models of chromospheric
condensations and show how the flare constrains electron heating
values and the development of flare layers in the chromospheres of M
dwarf stars.
Title: A 7-Day, Multiwavelength Flare Monitoring Campaign on AU Mic
Authors: Kowalski, Adam F.; Allred, Joel; Axelson, Roy; Brown,
Alexander; Carter, Brad; Grady, C. A.; Henry, Todd; Hinojosa, Rodrigo;
Jao, Wei-Chun; Lomax, Jamie L.; Neff, James E.; Osten, Rachel; Paredes,
Leonardo; Soutter, Jack; Schneider, Glenn; Vrijmoet, Eliot H.; White,
Graeme; Wisniewski, John
Bibcode: 2019AAS...23336014K
Altcode:
M dwarf flares exhibit a strong response in the X-ray and NUV, in line
with the standard Neupert effect observed in ~80% of (less energetic)
solar flares. However, some stellar flares produce only bright X-rays
and others only a bright NUV response. The detailed properties and
causes of each of these types of flares are not well constrained
because the vast majority of data of M dwarf flares in the past have
been in the optical without information at other wavelengths. Our
fundamental understanding of stellar flares has been hampered by
a lack of a large multi-wavelength dataset covering many types of
flares (Neupert vs. non-Neupert). We present first results from a
large flare campaign over ~7 days (Oct 10 - Oct 17, 2018) in which we
characterize AU Mic's flaring properties at X-ray, UV, optical, and
radio wavelengths. AU Mic is the brightest M dwarf flare star in the
sky, has a well-constrained (young) age, and is known to produce very
energetic flares on occasion. The flare monitoring was done with a large
fleet of ground and spaced-based observatories, including XMM-Newton,
Swift, the VLA, the ATCA, the SMARTS 0.9m and 1.5m telescopes at CTIO,
MINERVA-Australis, the ARC 3.5m at APO, and several sites in the LCO
Global Telescope Network. In each wavelength regime, we have devised
and made new measurements to probe the physics of flaring atmospheres
from the photosphere and/or low chromosphere through the corona. We show
how these data provide new constraints on radiative-hydrodynamic flare
models, and we discuss implications for the space weather in the system.
Title: A Hot Ultraviolet Flare on the M Dwarf Star GJ 674
Authors: Froning, C. S.; Kowalski, A.; France, K.; Loyd, R. O. Parke;
Schneider, P. Christian; Youngblood, A.; Wilson, D.; Brown, A.;
Berta-Thompson, Z.; Pineda, J. Sebastian; Linsky, J.; Rugheimer, S.;
Miguel, Y.
Bibcode: 2019arXiv190108647F
Altcode:
As part of the Mega MUSCLES Hubble Space Telescope (HST) Treasury
program, we obtained time-series ultraviolet spectroscopy of the
M2.5V star, GJ~674. During the FUV monitoring observations, the
target exhibited several small flares and one large flare (E_FUV =
10^{30.75} ergs) that persisted over the entirety of a HST orbit
and had an equivalent duration >30,000 sec, comparable to the
highest relative amplitude event previously recorded in the FUV. The
flare spectrum exhibited enhanced line emission from chromospheric,
transition region, and coronal transitions and a blue FUV continuum
with an unprecedented color temperature of T_c ~ 40,000+/-10,000
K. In this paper, we compare the flare FUV continuum emission with
parameterizations of radiative hydrodynamic model atmospheres of M star
flares. We find that the observed flare continuum can be reproduced
using flare models but only with the ad hoc addition of hot, dense
emitting component. This observation demonstrates that flares with hot
FUV continuum temperatures and significant EUV/FUV energy deposition
will continue to be of importance to exoplanet atmospheric chemistry
and heating even as the host M dwarfs age beyond their most active
evolutionary phases.
Title: Modeling of the Hydrogen Lyman Lines in Solar Flares
Authors: Brown, Stephen A.; Fletcher, Lyndsay; Kerr, Graham S.;
Labrosse, Nicolas; Kowalski, Adam F.; De La Cruz Rodríguez, Jaime
Bibcode: 2018ApJ...862...59B
Altcode: 2018arXiv180703373B
The hydrogen Lyman lines (91.2 nm < λ < 121.6 nm) are significant
contributors to the radiative losses of the solar chromosphere, and
they are enhanced during flares. We have shown previously that the Lyman
lines observed by the Extreme Ultraviolet Variability instrument onboard
the Solar Dynamics Observatory exhibit Doppler motions equivalent
to speeds on the order of 30 km s-1. However, contrary to
expectations, both redshifts and blueshifts were present and no dominant
flow direction was observed. To understand the formation of the Lyman
lines, particularly their Doppler motions, we have used the radiative
hydrodynamic code, RADYN, along with the radiative transfer code, RH,
to simulate the evolution of the flaring chromosphere and the response
of the Lyman lines during solar flares. We find that upflows in the
simulated atmospheres lead to blueshifts in the line cores, which
exhibit central reversals. We then model the effects of the instrument
on the profiles, using the Extreme Ultraviolet Variability Experiment
(EVE) instrument's properties. What may be interpreted as downflows
(redshifted emission) in the lines, after they have been convolved
with the instrumental line profile, may not necessarily correspond to
actual downflows. Dynamic features in the atmosphere can introduce
complex features in the line profiles that will not be detected by
instruments with the spectral resolution of EVE, but which leave more
of a signature at the resolution of the Spectral Investigation of the
Coronal Environment instrument onboard the Solar Orbiter.
Title: The Evolution of T = 10,000 K Blackbody-Like Continuum
Radiation in the Impulsive Phase of dMe Flares
Authors: Kowalski, Adam F.; Mathioudakis, Mihalis; Hawley, Suzanne L.
Bibcode: 2018csss.confE..42K
Altcode: 2018arXiv181007226K
The near-ultraviolet and optical (white-light) continuum radiation
in M dwarf flares exhibits a range of observed characteristics,
suggesting that the amount of heating at large optical depth varies
among impulsive-type and gradual-type flares. Specific flux ratios
from high-time cadence spectra and narrowband continuum photometry
have also shown that these characteristics vary from the peak to the
gradual decay phases of flares. In these proceedings, we present the
highest-time cadence ( 1 s), highest signal-to-noise ( 100) constraints
on the optical color temperature evolution during the rise phase of a
large, impulsive-type dMe flare event. The flare exhibits compelling
evidence of a hot, color temperature (T 10,000 K), but the Balmer jump
ratios show that the flare cannot be explained by isothermal slabs or
blackbody surfaces at any time in the evolution. The new data analysis
establish these properties as critical challenges for any flare model,
and we discuss 1D radiative-hydrodynamic modeling that will be compared
to the evolution of the flare colors in this intriguing event.
Title: IRIS Ultraviolet Spectral Properties of a Sample of X-Class
Solar Flares
Authors: Butler, Elizabeth; Kowalski, Adam; Cauzzi, Gianna; Allred,
Joel C.; Daw, Adrian N.
Bibcode: 2018AAS...23212101B
Altcode:
The white-light (near-ultraviolet (NUV) and optical) continuum emission
comprises the majority of the radiated energy in solar flares. However,
there are nearly as many explanations for the origin of the white-light
continuum radiation as there are white-light flares that have been
studied in detail with spectra. Furthermore, there are rarely robust
constraints on the time-resolved dynamics in the white-light emitting
flare layers. We are conducting a statistical study of the properties of
Fe II lines, Mg II lines, and NUV continuum intensity in bright flare
kernels observed by the Interface Region Imaging Spectrograph (IRIS),
in order to provide comprehensive constraints for radiative-hydrodynamic
flare models. Here we present a new technique for identifying bright
flare kernels and preliminary relationships among IRIS spectral
properties for a sample of X-class solar flares.
Title: A Phenomenological Two-Ribbon Model for Spatially Unresolved
Observations of Stellar Flares
Authors: Kowalski, Adam
Bibcode: 2018AAS...23231702K
Altcode:
Solar flares and flares that occur in much more magnetically
active stars share some striking properties, such as the observed
Neupert effect. However, stellar flares with the most impressive
multi-wavelength data sets are typically much more energetic
than solar flares, thus making robust connections difficult to
establish. Whereas solar data have the advantage of high spatial
resolution providing critical information about the development
of flare ribbons, the major advantage of stellar flare data is
the readily available broad-wavelength coverage of the white-light
radiation and the Balmer jump spectral region. Due to the lack of
direct spatial resolution for stellar flares and rarely coverage of
the Balmer jump region for solar flares, it is not clear how to make
a direct comparison. I will present a new method for modeling stellar
flares based on high spatial resolution information of solar flare
two-ribbon development for comparisons of the physics of their observed
phenomena, such as the red-wing asymmetries in chromospheric lines and
the white-light continuum radiation. The new modeling method combines
aspects of "multi-thread" modeling and 1D radiative-hydrodynamic
modeling. Our algorithm is important for interpreting the impulsive
phase of superflares in young G dwarfs in Kepler and understanding
how hour-long decay timescales are attained in the gradual phase of
some very energetic stellar flares.
Title: The Focusing Optics X-ray Solar Imager (FOXSI)
Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener,
Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Allred, Joel C.; Chen,
Bin; Battaglia, Marina; Drake, James Frederick; Gary, Dale E.; Goetz,
Keith; Gburek, Szymon; Grefenstette, Brian; Hannah, Iain G.; Holman,
Gordon; Hudson, Hugh S.; Inglis, Andrew R.; Ireland, Jack; Ishikawa,
Shin-nosuke; Klimchuk, James A.; Kontar, Eduard; Kowalski, Adam F.;
Massone, Anna Maria; Piana, Michele; Ramsey, Brian; Schwartz, Richard;
Steslicki, Marek; Ryan, Daniel; Warmuth, Alexander; Veronig, Astrid;
Vilmer, Nicole; White, Stephen M.; Woods, Thomas N.
Bibcode: 2018tess.conf40444C
Altcode:
We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer
(SMEX) Heliophysics mission that is currently undergoing a Phase A
concept study. FOXSI will provide a revolutionary new perspective on
energy release and particle acceleration on the Sun. FOXSI's primary
instrument, the Direct Spectroscopic Imager (DSI), is a direct imaging
X-ray spectrometer with higher dynamic range and better than 10x the
sensitivity of previous instruments. Flown on a 3-axis-stabilized
spacecraft in low-Earth orbit, DSI uses high-angular-resolution
grazing-incidence focusing optics combined with state-of-the-art
pixelated solid-state detectors to provide direct imaging of solar hard
X-rays for the first time. DSI is composed of a pair of X-ray telescopes
with a 14-meter focal length enabled by a deployable boom. DSI has a
field of view of 9 arcminutes and an angular resolution of better than 8
arcsec FWHM; it will cover the energy range from 3 up to 50-70 keV with
a spectral resolution of better than 1 keV. DSI will measure each photon
individually and will be able to create useful images at a sub-second
temporal resolution. FOXSI will also measure soft x-ray emission down
to 0.8 keV with a 0.25 keV resolution with its secondary instrument,
the Spectrometer for Temperature and Composition (STC) provided by
the Polish Academy of Sciences. Making use of an attenuator-wheel and
high-rate-capable detectors, FOXSI will be able to observe the largest
flares without saturation while still maintaining the sensitivity to
detect X-ray emission from weak flares, escaping electrons, and hot
active regions. This presentation will cover the data products and
software that can be expected from FOXSI and how they could be used
by the community.
Title: The Origin of White Light Flares: A parameter study of standard
model solar flare RHD Simulations
Authors: Kerr, Graham Stewart; de Aguiar Simoes, Paulo Jose; Fletcher,
Lyndsay; Allred, Joel C.; Kowalski, Adam F.
Bibcode: 2018tess.conf30490K
Altcode:
The bulk of the enhanced radiation emitted during solar flares
originates from the lower atmosphere, making it a crucial region for
understanding energy and radiation transport during flares. Of the
radiation emitted from the lower atmosphere a significant contribution
is from enhancements to the optical continuum (white light flares;
WLFs). There is still no consensus regarding the emission mechanism
responsible for WLFs, in part due to the paucity of broadband WLF
spectra, leading to ambiguity. Two commonly proposed mechanisms are
optically thin recombination radiation in the chromosphere resulting
from overionisation during the flare or optically thick radiation from
the photosphere/upper photosphere resulting from enhanced H- opacity
(an enhanced blackbody spectrum). Each mechanism can impose strong
constraints on models of energy transport. Of course a combination of
mechanisms is also possible. In the standard flare model, energy is
transported to the chromosphere via a beam of non-thermal electrons. To
address how WLFs would be produced in this standard model we performed
a parameter study, simulating 43 flares using RADYN, a radiation
hydrodynamics flare code. This study covered a range of typical
non-thermal electron beam distributions and energy fluxes. It was
found that in all cases the peak flare contribution to WLFs originated
in the upper chromosphere as a result of recombinations. For harder
non-thermal electron distributions there was also a non-negligible
contribution of H- emission from the lower chromosphere and upper
photosphere owing to an extended region of increased electron density
(itself resulting from stronger, more deeply penetrating, non-thermal
collisional ionisation rates). From this we predict that flares with a
harder non-thermal electron distribution may exhibit a larger vertical
extent when viewed on the limb. We were unable to simulate solely
optically thick sources of WLFs. Our simulated WLF spectra are in
good agreement with recent observations. Not all of our simulations
resulted in an observable WLF. In lower energy simulations, flare
energy input resulted in an enhanced opacity in the upper atmosphere
but without sufficient ionization/recombination to produce a strong
enough emissivity to counter the opacity. Thus we find that not all
flares are white light flares.
Title: The ngVLA's Role in Exoplanet Science: Constraining Exo-Space
Weather
Authors: Osten, Rachel A.; Crosley, Michael K.; Gudel, Manuel;
Kowalski, Adam F.; Lazio, Joe; Linsky, Jeffrey; Murphy, Eric; White,
Stephen
Bibcode: 2018arXiv180305345O
Altcode:
Radio observations are currently the only way to explore accelerated
particles in cool stellar environments. We describe how a next
generation VLA can contribute to the understanding of the stellar
contribution to exo-space weather. This area holds both academic and
popular interest, and is expected to grow in the next several decades.
Title: Detection of a Millimeter Flare from Proxima Centauri
Authors: MacGregor, Meredith A.; Weinberger, Alycia J.; Wilner,
David J.; Kowalski, Adam F.; Cranmer, Steven R.
Bibcode: 2018ApJ...855L...2M
Altcode: 2018arXiv180208257M
We present new analyses of ALMA 12 m and Atacama Compact Array (ACA)
observations at 233 GHz (1.3 mm) of the Proxima Centauri system with
sensitivities of 9.5 and 47 μJy beam-1, respectively,
taken from 2017 January 21 through April 25. These analyses reveal
that the star underwent a significant flaring event during one of
the ACA observations on 2017 March 24. The complete event lasted for
approximately 1 minute and reached a peak flux density of 100 ± 4 mJy,
nearly a factor of 1000 times brighter than the star’s quiescent
emission. At the flare peak, the continuum emission is characterized
by a steeply falling spectral index with frequency F ν
∝ ν α with α = -1.77 ± 0.45, and a lower limit on
the fractional linear polarization of | Q/I| =0.19+/- 0.02. Because
the ACA observations do not show any quiescent excess emission, we
conclude that there is no need to invoke the presence of a dust belt
at 1-4 au. We also posit that the slight excess flux density of 101 ±
9 μJy observed in the 12 m observations, compared to the photospheric
flux density of 74 ± 4 μJy extrapolated from infrared wavelengths,
may be due to coronal heating from continual smaller flares, as is
seen for AU Mic, another nearby well-studied M dwarf flare star. If
this is true, then the need for warm dust at ∼0.4 au is also removed.
Title: VizieR Online Data Catalog: MUSCLES Treasury Survey. IV. M
dwarf UV fluxes (Youngblood+, 2017)
Authors: Youngblood, A.; France, K.; Loyd, R. O. P.; Brown, A.;
Mason, J. P.; Schneider, P. C.; Tilley, M. A.; Berta-Thompson, Z. K.;
Buccino, A.; Froning, C. S.; Hawley, S. L.; Linsky, J.; Mauas,
P. J. D.; Redfield, S.; Kowalski, A.; Miguel, Y.; Newton, E. R.;
Rugheimer, S.; Segura, A.; Roberge, A.; Vieytes, M.
Bibcode: 2018yCat..18430031Y
Altcode:
We selected stars with HST UV spectra and ground-based optical spectra
either obtained directly by us or available in the VLT/XSHOOTER or
Keck/HIRES public archives. Several targets have spectroscopic
data obtained with the Dual Imaging Spectrograph (DIS) on the
ARC 3.5m telescope at Apache Point Observatory (APO), R~2500, or
the REOSC echelle spectrograph on the 2.15m telescope at Complejo
Astronomico El Leoncito (CASLEO), R~12000, within a day or two of
the HST observations. We also gathered spectra of GJ1132, GJ1214,
and Proxima Cen on the nights of 2016 March 7-9 using the MIKE echelle
spectrograph on the Magellan Clay telescope. (2 data files).
Title: The Mega-MUSCLES HST Treasury Survey
Authors: Froning, Cynthia S.; France, Kevin; Loyd, R. O. Parke;
Youngblood, Allison; Brown, Alexander; Schneider, Christian;
Berta-Thompson, Zachory; Kowalski, Adam
Bibcode: 2018AAS...23111105F
Altcode:
JWST will be able to observe the atmospheres of rocky planets transiting
nearby M dwarfs. A few such planets are already known (around GJ1132,
Proxima Cen, and Trappist-1) and TESS is predicted to find many more,
including ~14 habitable zone planets. To interpret observations of these
exoplanets' atmospheres, we must understand the high-energy SED of
their host stars: X-ray/EUV irradiation can erode a planet's gaseous
envelope and FUV/NUV-driven photochemistry shapes an atmosphere's
molecular abundances, including potential biomarkers like O2, O3, and
CH4. Our MUSCLES Treasury Survey (Cycles 19+22) used Hubble/COS+STIS
UV observations with contemporaneous X-ray and ground-based data to
construct complete SEDs for 11 low-mass exoplanet hosts. MUSCLES is
the most widely used database for early-M and K dwarf (>0.3 M_sun)
irradiance spectra and has supported a wide range of atmospheric
stability and biomarker modeling work. However, TESS will find most
of its habitable planets transiting stars less massive than this,
and these will be the planets to characterize with JWST. Here, we
introduce the Mega-MUSCLES project, an approved HST Cycle 25 Treasury
program. Following on the successful MUSCLES survey, Mega-MUSCLES will
expand our target list to focus on: (a) new M dwarf exoplanet hosts with
varying properties; (b) reference M dwarfs below 0.3 solar masses that
may be used as proxies for M dwarf planet hosts discovered after HST's
lifetime; and (c) more rapidly rotating stars of GJ1132's mass to probe
XUV evolution over gigayear timescales. We will also gather the first
panchromatic SEDs of rocky planet hosts GJ1132 and Trappist-1. Here,
we present an overview of the Mega-MUSCLES motivation, targets list,
and status of the survey and show how it extends proven methods to a
key new sample of stars, upon which critically depends the long-term
goal of studying habitable planet atmospheres with JWST and beyond.
Title: Parameterizations of Chromospheric Condensations in dG and
dMe Model Flare Atmospheres
Authors: Kowalski, Adam F.; Allred, Joel C.
Bibcode: 2018ApJ...852...61K
Altcode: 2017arXiv171109488K
The origin of the near-ultraviolet and optical continuum radiation
in flares is critical for understanding particle acceleration and
impulsive heating in stellar atmospheres. Radiative-hydrodynamic (RHD)
simulations in 1D have shown that high energy deposition rates from
electron beams produce two flaring layers at T ∼ 104 K
that develop in the chromosphere: a cooling condensation (downflowing
compression) and heated non-moving (stationary) flare layers just below
the condensation. These atmospheres reproduce several observed phenomena
in flare spectra, such as the red-wing asymmetry of the emission lines
in solar flares and a small Balmer jump ratio in M dwarf flares. The
high beam flux simulations are computationally expensive in 1D, and the
(human) timescales for completing NLTE models with adaptive grids in
3D will likely be unwieldy for some time to come. We have developed a
prescription for predicting the approximate evolved states, continuum
optical depth, and emergent continuum flux spectra of RHD model flare
atmospheres. These approximate prescriptions are based on an important
atmospheric parameter: the column mass ({m}{ref}) at which
hydrogen becomes nearly completely ionized at the depths that are
approximately in steady state with the electron beam heating. Using this
new modeling approach, we find that high energy flux density (>F11)
electron beams are needed to reproduce the brightest observed continuum
intensity in IRIS data of the 2014 March 29 X1 solar flare, and that
variation in {m}{ref} from 0.001 to 0.02 g cm-2
reproduces most of the observed range of the optical continuum flux
ratios at the peak of M dwarf flares.
Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission
Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.;
Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.;
Drake, J. F.; Gary, D. E.; Goetz, K.; Gburek, S.; Grefenstette, B.;
Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland,
J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.;
Massone, A. M.; Piana, M.; Ramsey, B.; Schwartz, R.; Steslicki, M.;
Turin, P.; Ryan, D.; Warmuth, A.; Veronig, A.; Vilmer, N.; White,
S. M.; Woods, T. N.
Bibcode: 2017AGUFMSH44A..07C
Altcode:
We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer
(SMEX) Heliophysics mission that is currently undergoing a Phase A
concept study. FOXSI will provide a revolutionary new perspective
on energy release and particle acceleration on the Sun. FOXSI is
a direct imaging X-ray spectrometer with higher dynamic range and
better than 10x the sensitivity of previous instruments. Flown
on a 3-axis-stabilized spacecraft in low-Earth orbit, FOXSI uses
high-angular-resolution grazing-incidence focusing optics combined
with state-of-the-art pixelated solid-state detectors to provide direct
imaging of solar hard X-rays for the first time. FOXSI is composed of
a pair of x-ray telescopes with a 14-meter focal length enabled by a
deployable boom. Making use of a filter-wheel and high-rate-capable
solid-state detectors, FOXSI will be able to observe the largest flares
without saturation while still maintaining the sensitivity to detect
x-ray emission from weak flares, escaping electrons, and hot active
regions. This mission concept is made possible by past experience with
similar instruments on two FOXSI sounding rocket flights, in 2012 and
2014, and on the HEROES balloon flight in 2013. FOXSI's hard X-ray
imager has a field of view of 9 arcminutes and an angular resolution
of better than 8 arcsec; it will cover the energy range from 3 up to
50-70 keV with a spectral resolution of better than 1 keV; and it will
have sub-second temporal resolution.
Title: Anticipated Results from the FOXSI SMEX Mission
Authors: Shih, A. Y.; Christe, S.; Krucker, S.; Glesener, L.;
Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.;
Drake, J. F.; Gary, D. E.; Gburek, S.; Goetz, K.; Grefenstette, B.;
Gubarev, M.; Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.;
Ireland, J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski,
A. F.; Massone, A. M.; Piana, M.; Ramsey, B.; Ryan, D.; Schwartz,
R.; Steslicki, M.; Turin, P.; Veronig, A.; Vilmer, N.; Warmuth, A.;
White, S. M.; Woods, T. N.
Bibcode: 2017AGUFMSH43C..03S
Altcode:
While there have been significant advances in our understanding
of impulsive energy release at the Sun since the advent of RHESSI
observations, there is a clear need for new X-ray observations that
can capture the full range of emission in flares (e.g., faint coronal
sources near bright chromospheric sources), follow the intricate
evolution of energy release and changes in morphology, and search
for the signatures of impulsive energy release in even the quiescent
Sun. The FOXSI Small Explorer (SMEX) mission, currently undergoing a
Phase A concept study, combines state-of-the-art grazing-incidence
focusing optics with pixelated solid-state detectors to provide
direct imaging of hard X-rays for the first time on a solar
observatory. FOXSI's X-ray observations will provide quantitative
information on (1) the non-thermal populations of accelerated electrons
and (2) the thermal plasma distributions at the high temperatures
inaccessible through other wavelengths. FOXSI's major science questions
include: Where are electrons accelerated and on what time scales? Where
do escaping flare-accelerated electrons originate? What is the energy
input of accelerated electrons into the chromosphere and corona? How
much do flare-like processes heat the corona above active regions? Here
we present examples with simulated observations to show how FOXSI's
capabilities will address and resolve these and other questions.
Title: A Unified Understanding of Flare Heating
Authors: Kowalski, Adam
Bibcode: 2017xmm..prop..101K
Altcode:
M dwarf flares exhibit a strong response in the X-ray and NUV,
in linewith the Neupert effect. However, some flares produce only
bright X-raysand others only a bright NUV response. Our fundamental
understanding ofstellar flares is therefore hampered by the lack of
multi-wavelengthdata. We propose a large XMM campaign to determine
the origin ofNeupert versus non-Neupert flares in AU Mic. The timing,
amplitude,and atmospheric parameters of the flares will determine
whether thedifferences are related to the relative roles of proton and
electronbeam heating. This study will also constrain the high-energy
tail of AUMic's flare frequency and hence enable a test of whether
the system'sdebris disk is experiencing space-weather.
Title: First Detection of a Strong Magnetic Field on a Bursty Brown
Dwarf: Puzzle Solved
Authors: Berdyugina, S. V.; Harrington, D. M.; Kuzmychov, O.; Kuhn,
J. R.; Hallinan, G.; Kowalski, A. F.; Hawley, S. L.
Bibcode: 2017ApJ...847...61B
Altcode: 2017arXiv170902861B
We report the first direct detection of a strong, 5 kG magnetic field on
the surface of an active brown dwarf. LSR J1835+3259 is an M8.5 dwarf
exhibiting transient radio and optical emission bursts modulated by
fast rotation. We have detected the surface magnetic field as circularly
polarized signatures in the 819 nm sodium lines when an active emission
region faced the Earth. Modeling Stokes profiles of these lines reveals
the effective temperature of 2800 K and log gravity acceleration of
4.5. These parameters place LSR J1835+3259 on evolutionary tracks as
a young brown dwarf with the mass of 55+/- 4{M}{{J}} and
age of 22 ± 4 Myr. Its magnetic field is at least 5.1 kG and covers
at least 11% of the visible hemisphere. The active region topology
recovered using line profile inversions comprises hot plasma loops with
a vertical stratification of optical and radio emission sources. These
loops rotate with the dwarf in and out of view causing periodic emission
bursts. The magnetic field is detected at the base of the loops. This
is the first time that we can quantitatively associate brown dwarf
non-thermal bursts with a strong, 5 kG surface magnetic field and
solve the puzzle of their driving mechanism. This is also the coolest
known dwarf with such a strong surface magnetic field. The young age
of LSR J1835+3259 implies that it may still maintain a disk, which may
facilitate bursts via magnetospheric accretion, like in higher-mass
T Tau-type stars. Our results pave a path toward magnetic studies of
brown dwarfs and hot Jupiters.
Title: Simulating the Mg II NUV Spectra & C II Resonance Lines
During Solar Flares
Authors: Kerr, Graham Stewart; Allred, Joel C.; Leenaarts, Jorrit;
Butler, Elizabeth; Kowalski, Adam
Bibcode: 2017SPD....48.0102K
Altcode:
The solar chromosphere is the origin of the bulk of the enhanced
radiative output during solar flares, and so comprehensive understanding
of this region is important if we wish to understand energy transport in
solar flares. It is only relatively recently, however, with the launch
of IRIS that we have routine spectroscopic flarea observations of the
chromsphere and transition region. Since several of the spectral lines
observed by IRIS are optically thick, it is necessary to use forward
modelling to extract the useful information that these lines carry about
the flaring chromosphere and transition region. We present the results
of modelling the formation properties Mg II resonance lines &
subordinate lines, and the C II resonance lines during solar flares. We
focus on understanding their relation to the physical strucutre of the
flaring atmosphere, exploiting formation height differences to determine
if we can extract information about gradients in the atmosphere. We
show the effect of degrading the profiles to the resolution of the
IRIS, and that the usual observational techniques used to identify
the line centroid do a poor job in the early stages of the flare
(partly due to multiple optically thick line components). Finally,
we will tentatively comment on the effects that 3D radiation transfer
may have on these lines.
Title: The MUSCLES Treasury Survey. IV. Scaling Relations for
Ultraviolet, Ca II K, and Energetic Particle Fluxes from M Dwarfs
Authors: Youngblood, Allison; France, Kevin; Loyd, R. O. Parke; Brown,
Alexander; Mason, James P.; Schneider, P. Christian; Tilley, Matt A.;
Berta-Thompson, Zachory K.; Buccino, Andrea; Froning, Cynthia S.;
Hawley, Suzanne L.; Linsky, Jeffrey; Mauas, Pablo J. D.; Redfield,
Seth; Kowalski, Adam; Miguel, Yamila; Newton, Elisabeth R.; Rugheimer,
Sarah; Segura, Antígona; Roberge, Aki; Vieytes, Mariela
Bibcode: 2017ApJ...843...31Y
Altcode: 2017arXiv170504361Y
Characterizing the UV spectral energy distribution (SED) of
an exoplanet host star is critically important for assessing its
planet’s potential habitability, particularly for M dwarfs, as they
are prime targets for current and near-term exoplanet characterization
efforts and atmospheric models predict that their UV radiation can
produce photochemistry on habitable zone planets different from that
on Earth. To derive ground-based proxies for UV emission for use when
Hubble Space Telescope (HST) observations are unavailable, we have
assembled a sample of 15 early to mid-M dwarfs observed by HST and
compared their nonsimultaneous UV and optical spectra. We find that
the equivalent width of the chromospheric Ca II K line at 3933 Å, when
corrected for spectral type, can be used to estimate the stellar surface
flux in ultraviolet emission lines, including H I Lyα. In addition,
we address another potential driver of habitability: energetic particle
fluxes associated with flares. We present a new technique for estimating
soft X-ray and >10 MeV proton flux during far-UV emission line flares
(Si IV and He II) by assuming solar-like energy partitions. We analyze
several flares from the M4 dwarf GJ 876 observed with HST and Chandra as
part of the MUSCLES Treasury Survey and find that habitable zone planets
orbiting GJ 876 are impacted by large Carrington-like flares with peak
soft X-ray fluxes ≥10-3 W m-2 and possible
proton fluxes ∼102-103 pfu, approximately four
orders of magnitude more frequently than modern-day Earth.
Title: Radio Optical Multiwavelength Stellar Flares and Constraints
on the Electron Population from a Joint Analysis
Authors: Osten, Rachel; Kowalski, Adam
Bibcode: 2017reph.conf40002O
Altcode:
The accelerated particles produced in stellar magnetic reconnection
events are important in shaping the habitable environment around the
star. Radio gyrosynchrotron flares trace the presence and action of
accelerated electrons high in the stellar atmosphere, while flares
observed at optical wavelengths probe the response lower in the stellar
atmosphere to the heating provided by electron beams. We present the
results of a several day multi wavelength observing campaign on the
nearby flare star EV Lac. The multifrequency radio observations probe
the non thermal particle energy and its dependence on the index of
the power-law distribution of particle energy as well as the magnetic
field strength, while optical observations constrain optical radiated
energy and limits on total bolometric flare radiated energy. We discuss
how the spectral shape of the optical flares can potentially constrain
the lower limit of the electron population, and what the coincidence
or lack thereof of simultaneously observed flares tells us about the
generalness of flare processes.
Title: Suppression of Hydrogen Emission in an X-class White-light
Solar Flare
Authors: Procházka, Ondřej; Milligan, Ryan O.; Allred, Joel C.;
Kowalski, Adam F.; Kotrč, Pavel; Mathioudakis, Mihalis
Bibcode: 2017ApJ...837...46P
Altcode: 2017arXiv170200638P
We present unique NUV observations of a well-observed X-class flare
from NOAA 12087 obtained at the Ondřejov Observatory. The flare
shows a strong white-light continuum but no detectable emission in
the higher Balmer and Lyman lines. Reuven Ramaty High-Energy Solar
Spectroscopic Imager and Fermi observations indicate an extremely
hard X-ray spectrum and γ-ray emission. We use the RADYN radiative
hydrodynamic code to perform two types of simulations: one where an
energy of 3 × 1011 erg cm-2 s-1
is deposited by an electron beam with a spectral index of ≈3, and a
second where the same energy is applied directly to the photosphere. The
combination of observations and simulations allows us to conclude
that the white-light emission and the suppression or complete lack
of hydrogen emission lines is best explained by a model where the
dominant energy deposition layer is located in the lower layers of
the solar atmosphere, rather than the chromosphere.
Title: Hydrogen Balmer Line Broadening in Solar and Stellar Flares
Authors: Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han; Tremblay,
Pier-Emmanuel; Brown, Stephen; Carlsson, Mats; Osten, Rachel A.;
Wisniewski, John P.; Hawley, Suzanne L.
Bibcode: 2017ApJ...837..125K
Altcode: 2017arXiv170203321K
The broadening of the hydrogen lines during flares is thought to
result from increased charge (electron, proton) density in the flare
chromosphere. However, disagreements between theory and modeling
prescriptions have precluded an accurate diagnostic of the degree
of ionization and compression resulting from flare heating in the
chromosphere. To resolve this issue, we have incorporated the unified
theory of electric pressure broadening of the hydrogen lines into
the non-LTE radiative-transfer code RH. This broadening prescription
produces a much more realistic spectrum of the quiescent, A0 star Vega
compared to the analytic approximations used as a damping parameter
in the Voigt profiles. We test recent radiative-hydrodynamic (RHD)
simulations of the atmospheric response to high nonthermal electron
beam fluxes with the new broadening prescription and find that
the Balmer lines are overbroadened at the densest times in the
simulations. Adding many simultaneously heated and cooling model
loops as a “multithread” model improves the agreement with the
observations. We revisit the three-component phenomenological flare
model of the YZ CMi Megaflare using recent and new RHD models. The
evolution of the broadening, line flux ratios, and continuum flux
ratios are well-reproduced by a multithread model with high-flux
nonthermal electron beam heating, an extended decay phase model, and a
“hot spot” atmosphere heated by an ultrarelativistic electron beam
with reasonable filling factors: ∼0.1%, 1%, and 0.1% of the visible
stellar hemisphere, respectively. The new modeling motivates future
work to understand the origin of the extended gradual phase emission.
Title: The Atmospheric Response to High Nonthermal Electron Beam
Fluxes in Solar Flares. I. Modeling the Brightest NUV Footpoints in
the X1 Solar Flare of 2014 March 29
Authors: Kowalski, Adam F.; Allred, Joel C.; Daw, Adrian; Cauzzi,
Gianna; Carlsson, Mats
Bibcode: 2017ApJ...836...12K
Altcode: 2016arXiv160907390K
The 2014 March 29 X1 solar flare (SOL20140329T17:48) produced bright
continuum emission in the far- and near-ultraviolet (NUV) and highly
asymmetric chromospheric emission lines, providing long-sought
constraints on the heating mechanisms of the lower atmosphere in
solar flares. We analyze the continuum and emission line data from
the Interface Region Imaging Spectrograph (IRIS) of the brightest
flaring magnetic footpoints in this flare. We compare the NUV spectra
of the brightest pixels to new radiative-hydrodynamic predictions
calculated with the RADYN code using constraints on a nonthermal
electron beam inferred from the collisional thick-target modeling of
hard X-ray data from Reuven Ramaty High Energy Solar Spectroscopic
Imager. We show that the atmospheric response to a high beam flux
density satisfactorily achieves the observed continuum brightness
in the NUV. The NUV continuum emission in this flare is consistent
with hydrogen (Balmer) recombination radiation that originates from
low optical depth in a dense chromospheric condensation and from the
stationary beam-heated layers just below the condensation. A model
producing two flaring regions (a condensation and stationary layers)
in the lower atmosphere is also consistent with the asymmetric Fe II
chromospheric emission line profiles observed in the impulsive phase.
Title: Solar Ellerman Bombs in 1D Radiative Hydrodynamics
Authors: Reid, A.; Mathioudakis, M.; Kowalski, A.; Doyle, J. G.;
Allred, J. C.
Bibcode: 2017ApJ...835L..37R
Altcode: 2017arXiv170104213R
Recent observations from the Interface Region Imaging Spectrograph
appear to show impulsive brightenings in high temperature lines,
which when combined with simultaneous ground-based observations in
Hα, appear co-spatial to Ellerman Bombs (EBs). We use the RADYN
one-dimensional radiative transfer code in an attempt to try and
reproduce the observed line profiles and simulate the atmospheric
conditions of these events. Combined with the MULTI/RH line synthesis
codes, we compute the Hα, Ca II 8542 Å, and Mg II h and k lines for
these simulated events and compare them to previous observations. Our
findings hint that the presence of superheated regions in the
photosphere (>10,000 K) is not a plausible explanation for the
production of EB signatures. While we are able to recreate EB-like
line profiles in Hα, Ca II 8542 Å, and Mg II h and k, we cannot
achieve agreement with all of these simultaneously.
Title: Exploring impulsive solar magnetic energy release and particle
acceleration with focused hard X-ray imaging spectroscopy
Authors: Christe, Steven; Krucker, Samuel; Glesener, Lindsay; Shih,
Albert; Saint-Hilaire, Pascal; Caspi, Amir; Allred, Joel; Battaglia,
Marina; Chen, Bin; Drake, James; Dennis, Brian; Gary, Dale; Gburek,
Szymon; Goetz, Keith; Grefenstette, Brian; Gubarev, Mikhail; Hannah,
Iain; Holman, Gordon; Hudson, Hugh; Inglis, Andrew; Ireland, Jack;
Ishikawa, Shinosuke; Klimchuk, James; Kontar, Eduard; Kowalski, Adam;
Longcope, Dana; Massone, Anna-Maria; Musset, Sophie; Piana, Michele;
Ramsey, Brian; Ryan, Daniel; Schwartz, Richard; Stęślicki, Marek;
Turin, Paul; Warmuth, Alexander; Wilson-Hodge, Colleen; White, Stephen;
Veronig, Astrid; Vilmer, Nicole; Woods, Tom
Bibcode: 2017arXiv170100792C
Altcode:
How impulsive magnetic energy release leads to solar eruptions and how
those eruptions are energized and evolve are vital unsolved problems
in Heliophysics. The standard model for solar eruptions summarizes
our current understanding of these events. Magnetic energy in the
corona is released through drastic restructuring of the magnetic
field via reconnection. Electrons and ions are then accelerated by
poorly understood processes. Theories include contracting loops,
merging magnetic islands, stochastic acceleration, and turbulence at
shocks, among others. Although this basic model is well established,
the fundamental physics is poorly understood. HXR observations
using grazing-incidence focusing optics can now probe all of the key
regions of the standard model. These include two above-the-looptop
(ALT) sources which bookend the reconnection region and are likely
the sites of particle acceleration and direct heating. The science
achievable by a direct HXR imaging instrument can be summarized by the
following science questions and objectives which are some of the most
outstanding issues in solar physics (1) How are particles accelerated
at the Sun? (1a) Where are electrons accelerated and on what time
scales? (1b) What fraction of electrons is accelerated out of the
ambient medium? (2) How does magnetic energy release on the Sun lead
to flares and eruptions? A Focusing Optics X-ray Solar Imager (FOXSI)
instrument, which can be built now using proven technology and at modest
cost, would enable revolutionary advancements in our understanding of
impulsive magnetic energy release and particle acceleration, a process
which is known to occur at the Sun but also throughout the Universe.
Title: A Chromospheric Flare Model Consisting of Two Dynamical Layers:
Critical Tests from IRIS Data of Solar Flares
Authors: Kowalski, Adam; Allred, Joel C.; Daw, Adrian N.; Cauzzi,
Gianna; Carlsson, Mats; Inglis, Andrew; O'Neill, Aaron; Mathioudakis,
Mihalis; Uitenbroek, Han
Bibcode: 2017AAS...22933902K
Altcode:
Recent 1D radiative-hydrodynamic simulations of flares have shown that
a heated, chromospheric compression layer and a stationary layer, just
below the compression, are produced in response to high flux electron
beam heating. The hot blackbody-like continuum and redshifted intensity
in singly ionized chromospheric lines in these model predictions are
generally consistent with broad wavelength coverage spectra of M dwarf
flares and with high spectral resolution observations of solar flares,
respectively. We critically test this two-component chromospheric
flare model against the Fe II profiles and NUV continuum brightness
for several X-class solar flares observed with the Interface Region
Imaging Spectrograph (IRIS). We present several new predictions for
the Daniel K. Inoue Solar Telescope (DKIST).
Title: Observations and Simulations of the Na I D1 Line
Profiles in an M-class Solar Flare
Authors: Kuridze, D.; Mathioudakis, M.; Christian, D. J.; Kowalski,
A. F.; Jess, D. B.; Grant, S. D. T.; Kawate, T.; Simões, P. J. A.;
Allred, J. C.; Keenan, F. P.
Bibcode: 2016ApJ...832..147K
Altcode: 2016arXiv160908120K
We study the temporal evolution of the Na I D1 line profiles
in the M3.9 flare SOL2014-06-11T21:03 UT, using observations at high
spectral resolution obtained with the Interferometric Bidimensional
Spectrometer instrument on the Dunn Solar Telescope combined with
radiative hydrodynamic simulations. Our results show a significant
increase in the intensities of the line core and wings during the
flare. The analysis of the line profiles from the flare ribbons
reveals that the Na I D1 line has a central reversal
with excess emission in the blue wing (blue asymmetry). We combine
RADYN and RH simulations to synthesize Na I D1 line
profiles of the flaring atmosphere and find good agreement with
the observations. Heating with a beam of electrons modifies the
radiation field in the flaring atmosphere and excites electrons
from the ground state 3s 2S to the first excited state 3p
2P, which in turn modifies the relative population of the
two states. The change in temperature and the population density of
the energy states make the sodium line profile revert from absorption
into emission. Furthermore, the rapid changes in temperature break the
pressure balance between the different layers of the lower atmosphere,
generating upflow/downflow patterns. Analysis of the simulated spectra
reveals that the asymmetries of the Na I D1 flare profile
are produced by the velocity gradients in the lower solar atmosphere.
Title: Suppression of Hydrogen Emission in a White-light Solar Flare
Authors: Milligan, R. O.; Procházka, O.; Mathioudakis, M.; Allred,
J. C.; Kowalski, A. F.
Bibcode: 2016AGUFMSH31B2561P
Altcode: 2016AGUFMSH31B2561M
We present an analysis of an X-class flare that occurred on 11
June 2014 in active region NOAA 12087 using a newly developed high
cadence Image Selector operated by Astronomical Institute in Ondrejov,
Czech Republic. This instrument provides spectra in the 350-440 nm
wavelength range, which covers the higher order Balmer lines as well
as the Balmer jump at 364 nm. However, no detectable increase in these
emissions were detected during the flare, and support observations from
SDO/EVE MEGS-B also show that the Lyman line series and recombination
continuum were also suppressed, particularly when compared to two
other X-class flares on the preceding day. The X-class flare under
investigation also showed strong white light emission in SDO/HMI
data, as well as an extremely hard electron spectrum (delta 3.6),
and gamma-ray emission, from RHESSI data. This unique combination
of datasets was amended with radiative hydrodynamic model of direct
minimum temperature region heating. The results allow us to conclude
that the white light emission from this flare corresponds to a black
body heated by high-energy electrons (and/or ions), as opposed to
optical chromospheric emission from hydrogen.
Title: Investigating the Effects of Stark Broadening in the Balmer
Lines Observed in Solar Flares
Authors: Allred, J. C.; Kowalski, A. F.
Bibcode: 2016AGUFMSH43E..04A
Altcode:
During solar flares, the ambient electron density in the region where
Balmer lines form can be elevated by several orders of magnitude,
resulting in dramatically broadened lines due to the linear Stark
effect. In fact, modeling these broadened line profiles can provide a
direct measurement of the flaring chromosphere electron density. This
diagnostic is useful for determining atmospheric stratification
in flaring loops. Here we present results from a radiative transfer
model based on the RH code (Uitenbroek 2001) that has been enhanced to
include the Vidal, Cooper and Smith (1973; VCS) unified Stark broadening
theory. We find that in flaring conditions previous models significantly
underestimate the broadening in Balmer lines. We use our simulations
to predict Balmer decrements and show how matching line profiles with
observations constrains the flaring chromospheric electron density.
Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission
Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.;
Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen,
B.; Drake, J. F.; Gary, D. E.; Goetz, K.; Grefenstette, B.; Hannah,
I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland, J.; Ishikawa,
S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.; Massone, A. M.;
Piana, M.; Ramsey, B.; Gubarev, M.; Schwartz, R. A.; Steslicki, M.;
Ryan, D.; Turin, P.; Warmuth, A.; White, S. M.; Veronig, A.; Vilmer,
N.; Dennis, B. R.
Bibcode: 2016AGUFMSH13A2281C
Altcode:
We present FOXSI (Focusing Optics X-ray Solar Imager), a recently
proposed Small Explorer (SMEX) mission that will provide a revolutionary
new perspective on energy release and particle acceleration on the
Sun. FOXSI is a direct imaging X-ray spectrometer with higher dynamic
range and better than 10x the sensitivity of previous instruments. Flown
on a 3-axis stabilized spacecraft in low-Earth orbit, FOXSI uses
high-angular-resolution grazing-incidence focusing optics combined
with state-of-the-art pixelated solid-state detectors to provide direct
imaging of solar hard X-rays for the first time. FOXSI is composed of
two individual x-ray telescopes with a 14-meter focal length enabled by
a deployable boom. Making use of a filter-wheel and high-rate-capable
solid-state detectors, FOXSI will be able to observe the largest flares
without saturation while still maintaining the sensitivity to detect
x-ray emission from weak flares, escaping electrons, and hot active
regions. This SMEX mission is made possible by past experience with
similar instruments on two sounding rocket flights, in 2012 and 2014,
and on the HEROES balloon flight in 2013. FOXSI will image the Sun
with a field of view of 9 arcminutes and an angular resolution of
better than 8 arcsec; it will cover the energy range from 3 to 100
keV with a spectral resolution of better than 1 keV; and it will have
sub-second temporal resolution.
Title: A Very Bright, Very Hot, and Very Long Flaring Event from
the M Dwarf Binary System DG CVn
Authors: Osten, Rachel A.; Kowalski, Adam; Drake, Stephen A.; Krimm,
Hans; Page, Kim; Gazeas, Kosmas; Kennea, Jamie; Oates, Samantha;
Page, Mathew; de Miguel, Enrique; Novák, Rudolf; Apeltauer, Tomas;
Gehrels, Neil
Bibcode: 2016ApJ...832..174O
Altcode: 2016arXiv160904674O
On 2014 April 23, the Swift satellite responded to a hard X-ray
transient detected by its Burst Alert Telescope, which turned out to
be a stellar flare from a nearby, young M dwarf binary DG CVn. We
utilize observations at X-ray, UV, optical, and radio wavelengths
to infer the properties of two large flares. The X-ray spectrum of
the primary outburst can be described over the 0.3-100 keV bandpass
by either a single very high-temperature plasma or a nonthermal
thick-target bremsstrahlung model, and we rule out the nonthermal
model based on energetic grounds. The temperatures were the highest
seen spectroscopically in a stellar flare, at T X of
290 MK. The first event was followed by a comparably energetic event
almost a day later. We constrain the photospheric area involved in
each of the two flares to be >1020 cm2, and
find evidence from flux ratios in the second event of contributions
to the white light flare emission in addition to the usual hot, T ∼
104 K blackbody emission seen in the impulsive phase of
flares. The radiated energy in X-rays and white light reveal these
events to be the two most energetic X-ray flares observed from an M
dwarf, with X-ray radiated energies in the 0.3-10 keV bandpass of 4
× 1035 and 9 × 1035 erg, and optical flare
energies at E V of 2.8 × 1034 and 5.2 ×
1034 erg, respectively. The results presented here should
be integrated into updated modeling of the astrophysical impact of
large stellar flares on close-in exoplanetary atmospheres.
Title: Kepler Flares. IV. A Comprehensive Analysis of the Activity
of the dM4e Star GJ 1243
Authors: Silverberg, Steven M.; Kowalski, Adam F.; Davenport, James
R. A.; Wisniewski, John P.; Hawley, Suzanne L.; Hilton, Eric J.
Bibcode: 2016ApJ...829..129S
Altcode: 2016arXiv160703886S
We present a comprehensive study of the active dM4e star GJ 1243. We
use previous observations and ground-based echelle spectroscopy
to determine that GJ 1243 is a member of the Argus association of
field stars, suggesting it is ∼ 30{--}50 {{Myr}} old. We analyze 11
months of 1 minute cadence data from Kepler, presenting Kepler flare
frequency distributions, as well as determining correlations between
flare energy, amplitude, duration, and decay time. We find that the
exponent α of the power-law flare energy distribution varies in
time, primarily due to completeness of sample and the low frequency
of high-energy flares. We also find a deviation from a single power
law at high energy. We use ground-based spectroscopic observations
that were simultaneous with the Kepler data to provide simultaneous
photometric and spectroscopic analysis of three low-energy flares,
the lowest-energy dMe flares with detailed spectral analysis to date on
any star. The spectroscopic data from these flares extend constraints
for radiative hydrodynamic flare models to a lower energy regime than
has previously been studied. We use this simultaneous spectroscopy and
Kepler photometry to develop approximate conversions from the Kepler
bandpass to the traditional U and B bands. This conversion will be a
critical factor in comparing any Kepler flare analyses to the canon
of previous ground-based flare studies.
Title: The Characteristics of Solar X-Class Flares and CMEs: A
Paradigm for Stellar Superflares and Eruptions?
Authors: Harra, Louise K.; Schrijver, Carolus J.; Janvier, Miho;
Toriumi, Shin; Hudson, Hugh; Matthews, Sarah; Woods, Magnus M.; Hara,
Hirohisa; Guedel, Manuel; Kowalski, Adam; Osten, Rachel; Kusano,
Kanya; Lueftinger, Theresa
Bibcode: 2016SoPh..291.1761H
Altcode: 2016SoPh..tmp..111H
This paper explores the characteristics of 42 solar X-class flares that
were observed between February 2011 and November 2014, with data from
the Solar Dynamics Observatory (SDO) and other sources. This flare
list includes nine X-class flares that had no associated CMEs. In
particular our aim was to determine whether a clear signature could
be identified to differentiate powerful flares that have coronal
mass ejections (CMEs) from those that do not. Part of the motivation
for this study is the characterization of the solar paradigm for
flare/CME occurrence as a possible guide to the stellar observations;
hence we emphasize spectroscopic signatures. To do this we ask the
following questions: Do all eruptive flares have long durations? Do
CME-related flares stand out in terms of active-region size vs. flare
duration? Do flare magnitudes correlate with sunspot areas, and, if so,
are eruptive events distinguished? Is the occurrence of CMEs related to
the fraction of the active-region area involved? Do X-class flares with
no eruptions have weaker non-thermal signatures? Is the temperature
dependence of evaporation different in eruptive and non-eruptive
flares? Is EUV dimming only seen in eruptive flares? We find only one
feature consistently associated with CME-related flares specifically:
coronal dimming in lines characteristic of the quiet-Sun corona,
i.e. 1 - 2 MK. We do not find a correlation between flare magnitude
and sunspot areas. Although challenging, it will be of importance to
model dimming for stellar cases and make suitable future plans for
observations in the appropriate wavelength range in order to identify
stellar CMEs consistently.
Title: Flares In Time-Domain Surveys
Authors: Kowalski, Adam; Hawley, Suzanne; Davenport, James; Berlicki,
Arkadiusz; Cauzzi, Gianna; Fletcher, Lyndsay; Heinzel, Petr; Notsu,
Yuta; Loyd, Parke; Martinez Oliveros, Juan Carlos; Pugh, Chloe;
Schmidt, Sarah Jane; Karmakar, Subhajeet; Pye, John; Flaccomio, Ettore
Bibcode: 2016csss.confE.126K
Altcode:
Proceedings for the splinter session "Flares in Time-Domain Surveys"
convened at Cool Stars 19 on June 07, 2016 in Uppsala, Sweden. Contains
a two page summary of the splinter session, links to YouTube talks,
and a PDF copy of the slides from the presenters.
Title: Advances In Understanding Solar And Stellar Flares
Authors: Kowalski, Adam F.
Bibcode: 2016csss.confE.127K
Altcode:
Flares result from the sudden reconnection and relaxation of magnetic
fields in the coronae of stellar atmospheres. The highly dynamic
atmospheric response produces radiation across the electromagnetic
spectrum, from the radio to X-rays, on a range of timescales,
from seconds to days. New high resolution data of solar flares have
revealed the intrinsic spatial properties of the flaring chromosphere,
which is thought to be where the majority of the flare energy
is released as radiation in the optical and near-UV continua and
emission lines. New data of stellar flares have revealed the detailed
properties of the broadband (white-light) continuum emission, which
provides straightforward constraints for models of the transformation
of stored magnetic energy in the corona into thermal energy of the
lower atmosphere. In this talk, we discuss the physical processes that
produce several important spectral phenomena in the near-ultraviolet
and optical as revealed from new radiative-hydrodynamic models of
flares on the Sun and low mass stars. We present recent progress
with high-flux nonthermal electron beams in reproducing the observed
optical continuum color temperature of T 10,000 K and the Balmer
jump properties in the near-ultraviolet. These beams produce dense,
heated chromospheric condensations, which can explain the shape and
strength of the continuum emission in M dwarf flares and the red-wing
asymmetries in the chromospheric emission lines in recent observations
of solar flares from the Interface Region Imaging Spectrograph. Current
theoretical challenges and future modeling directions will be discussed,
as well as observational synergies between solar and stellar flares.
Title: The LOFT mission concept: a status update
Authors: Feroci, M.; Bozzo, E.; Brandt, S.; Hernanz, M.; van der Klis,
M.; Liu, L. -P.; Orleanski, P.; Pohl, M.; Santangelo, A.; Schanne, S.;
Stella, L.; Takahashi, T.; Tamura, H.; Watts, A.; Wilms, J.; Zane,
S.; Zhang, S. -N.; Bhattacharyya, S.; Agudo, I.; Ahangarianabhari,
M.; Albertus, C.; Alford, M.; Alpar, A.; Altamirano, D.; Alvarez,
L.; Amati, L.; Amoros, C.; Andersson, N.; Antonelli, A.; Argan, A.;
Artigue, R.; Artigues, B.; Atteia, J. -L.; Azzarello, P.; Bakala, P.;
Ballantyne, D.; Baldazzi, G.; Baldo, M.; Balman, S.; Barbera, M.; van
Baren, C.; Barret, D.; Baykal, A.; Begelman, M.; Behar, E.; Behar, O.;
Belloni, T.; Bernardini, F.; Bertuccio, G.; Bianchi, S.; Bianchini,
A.; Binko, P.; Blay, P.; Bocchino, F.; Bode, M.; Bodin, P.; Bombaci,
I.; Bonnet Bidaud, J. -M.; Boutloukos, S.; Bouyjou, F.; Bradley, L.;
Braga, J.; Briggs, M. S.; Brown, E.; Buballa, M.; Bucciantini, N.;
Burderi, L.; Burgay, M.; Bursa, M.; Budtz-Jørgensen, C.; Cackett,
E.; Cadoux, F.; Cais, P.; Caliandro, G. A.; Campana, R.; Campana,
S.; Cao, X.; Capitanio, F.; Casares, J.; Casella, P.; Castro-Tirado,
A. J.; Cavazzuti, E.; Cavechi, Y.; Celestin, S.; Cerda-Duran, P.;
Chakrabarty, D.; Chamel, N.; Château, F.; Chen, C.; Chen, Y.; Chen,
Y.; Chenevez, J.; Chernyakova, M.; Coker, J.; Cole, R.; Collura,
A.; Coriat, M.; Cornelisse, R.; Costamante, L.; Cros, A.; Cui, W.;
Cumming, A.; Cusumano, G.; Czerny, B.; D'Aı, A.; D'Ammando, F.;
D'Elia, V.; Dai, Z.; Del Monte, E.; De Luca, A.; De Martino, D.;
Dercksen, J. P. C.; De Pasquale, M.; De Rosa, A.; Del Santo, M.; Di
Cosimo, S.; Degenaar, N.; den Herder, J. W.; Diebold, S.; Di Salvo,
T.; Dong, Y.; Donnarumma, I.; Doroshenko, V.; Doyle, G.; Drake, S. A.;
Durant, M.; Emmanoulopoulos, D.; Enoto, T.; Erkut, M. H.; Esposito,
P.; Evangelista, Y.; Fabian, A.; Falanga, M.; Favre, Y.; Feldman, C.;
Fender, R.; Feng, H.; Ferrari, V.; Ferrigno, C.; Finger, M.; Finger,
M. H.; Fraser, G. W.; Frericks, M.; Fullekrug, M.; Fuschino, F.;
Gabler, M.; Galloway, D. K.; Gálvez Sanchez, J. L.; Gandhi, P.; Gao,
Z.; Garcia-Berro, E.; Gendre, B.; Gevin, O.; Gezari, S.; Giles, A. B.;
Gilfanov, M.; Giommi, P.; Giovannini, G.; Giroletti, M.; Gogus, E.;
Goldwurm, A.; Goluchová, K.; Götz, D.; Gou, L.; Gouiffes, C.; Grandi,
P.; Grassi, M.; Greiner, J.; Grinberg, V.; Groot, P.; Gschwender, M.;
Gualtieri, L.; Guedel, M.; Guidorzi, C.; Guy, L.; Haas, D.; Haensel,
P.; Hailey, M.; Hamuguchi, K.; Hansen, F.; Hartmann, D. H.; Haswell,
C. A.; Hebeler, K.; Heger, A.; Hempel, M.; Hermsen, W.; Homan, J.;
Hornstrup, A.; Hudec, R.; Huovelin, J.; Huppenkothen, D.; Inam, S. C.;
Ingram, A.; In't Zand, J. J. M.; Israel, G.; Iwasawa, K.; Izzo, L.;
Jacobs, H. M.; Jetter, F.; Johannsen, T.; Jenke, P. A.; Jonker, P.;
Josè, J.; Kaaret, P.; Kalamkar, K.; Kalemci, E.; Kanbach, G.; Karas,
V.; Karelin, D.; Kataria, D.; Keek, L.; Kennedy, T.; Klochkov, D.;
Kluzniak, W.; Koerding, E.; Kokkotas, K.; Komossa, S.; Korpela, S.;
Kouveliotou, C.; Kowalski, A. F.; Kreykenbohm, I.; Kuiper, L. M.;
Kunneriath, D.; Kurkela, A.; Kuvvetli, I.; La Franca, F.; Labanti,
C.; Lai, D.; Lamb, F. K.; Lachaud, C.; Laubert, P. P.; Lebrun, F.;
Li, X.; Liang, E.; Limousin, O.; Lin, D.; Linares, M.; Linder, D.;
Lodato, G.; Longo, F.; Lu, F.; Lund, N.; Maccarone, T. J.; Macera,
D.; Maestre, S.; Mahmoodifar, S.; Maier, D.; Malcovati, P.; Malzac,
J.; Malone, C.; Mandel, I.; Mangano, V.; Manousakis, A.; Marelli, M.;
Margueron, J.; Marisaldi, M.; Markoff, S. B.; Markowitz, A.; Marinucci,
A.; Martindale, A.; Martínez, G.; McHardy, I. M.; Medina-Tanco, G.;
Mehdipour, M.; Melatos, A.; Mendez, M.; Mereghetti, S.; Migliari,
S.; Mignani, R.; Michalska, M.; Mihara, T.; Miller, M. C.; Miller,
J. M.; Mineo, T.; Miniutti, G.; Morsink, S.; Motch, C.; Motta, S.;
Mouchet, M.; Mouret, G.; Mulačová, J.; Muleri, F.; Muñoz-Darias,
T.; Negueruela, I.; Neilsen, J.; Neubert, T.; Norton, A. J.; Nowak,
M.; Nucita, A.; O'Brien, P.; Oertel, M.; Olsen, P. E. H.; Orienti, M.;
Orio, M.; Orlandini, M.; Osborne, J. P.; Osten, R.; Ozel, F.; Pacciani,
L.; Paerels, F.; Paltani, S.; Paolillo, M.; Papadakis, I.; Papitto,
A.; Paragi, Z.; Paredes, J. M.; Patruno, A.; Paul, B.; Pederiva, F.;
Perinati, E.; Pellizzoni, A.; Penacchioni, A. V.; Peretz, U.; Perez,
M. A.; Perez-Torres, M.; Peterson, B. M.; Petracek, V.; Pittori,
C.; Pons, J.; Portell, J.; Possenti, A.; Postnov, K.; Poutanen, J.;
Prakash, M.; Prandoni, I.; Le Provost, H.; Psaltis, D.; Pye, J.; Qu,
J.; Rambaud, D.; Ramon, P.; Ramsay, G.; Rapisarda, M.; Rashevski,
A.; Rashevskaya, I.; Ray, P. S.; Rea, N.; Reddy, S.; Reig, P.; Reina
Aranda, M.; Remillard, R.; Reynolds, C.; Rezzolla, L.; Ribo, M.; de
la Rie, R.; Riggio, A.; Rios, A.; Rischke, D. H.; Rodríguez-Gil, P.;
Rodriguez, J.; Rohlfs, R.; Romano, P.; Rossi, E. M. R.; Rozanska, A.;
Rousseau, A.; Rudak, B.; Russell, D. M.; Ryde, F.; Sabau-Graziati,
L.; Sakamoto, T.; Sala, G.; Salvaterra, R.; Salvetti, D.; Sanna, A.;
Sandberg, J.; Savolainen, T.; Scaringi, S.; Schaffner-Bielich, J.;
Schatz, H.; Schee, J.; Schmid, C.; Serino, M.; Shakura, N.; Shore,
S.; Schnittman, J. D.; Schneider, R.; Schwenk, A.; Schwope, A. D.;
Sedrakian, A.; Seyler, J. -Y.; Shearer, A.; Slowikowska, A.; Sims,
M.; Smith, A.; Smith, D. M.; Smith, P. J.; Sobolewska, M.; Sochora,
V.; Soffitta, P.; Soleri, P.; Song, L.; Spencer, A.; Stamerra,
A.; Stappers, B.; Staubert, R.; Steiner, A. W.; Stergioulas, N.;
Stevens, A. L.; Stratta, G.; Strohmayer, T. E.; Stuchlik, Z.; Suchy,
S.; Suleimanov, V.; Tamburini, F.; Tauris, T.; Tavecchio, F.; Tenzer,
C.; Thielemann, F. K.; Tiengo, A.; Tolos, L.; Tombesi, F.; Tomsick, J.;
Torok, G.; Torrejon, J. M.; Torres, D. F.; Torresi, E.; Tramacere, A.;
Traulsen, I.; Trois, A.; Turolla, R.; Turriziani, S.; Typel, S.; Uter,
P.; Uttley, P.; Vacchi, A.; Varniere, P.; Vaughan, S.; Vercellone,
S.; Vietri, M.; Vincent, F. H.; Vrba, V.; Walton, D.; Wang, J.; Wang,
Z.; Watanabe, S.; Wawrzaszek, R.; Webb, N.; Weinberg, N.; Wende, H.;
Wheatley, P.; Wijers, R.; Wijnands, R.; Wille, M.; Wilson-Hodge,
C. A.; Winter, B.; Walk, S. J.; Wood, K.; Woosley, S. E.; Wu, X.;
Xu, R.; Yu, W.; Yuan, F.; Yuan, W.; Yuan, Y.; Zampa, G.; Zampa, N.;
Zampieri, L.; Zdunik, L.; Zdziarski, A.; Zech, A.; Zhang, B.; Zhang,
C.; Zhang, S.; Zingale, M.; Zwart, F.
Bibcode: 2016SPIE.9905E..1RF
Altcode:
The Large Observatory For x-ray Timing (LOFT) is a mission concept
which was proposed to ESA as M3 and M4 candidate in the framework of the
Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination
of effective area and spectral resolution of its main instrument and
the uniquely large field of view of its wide field monitor, LOFT will
be able to study the behaviour of matter in extreme conditions such
as the strong gravitational field in the innermost regions close to
black holes and neutron stars and the supra-nuclear densities in
the interiors of neutron stars. The science payload is based on a
Large Area Detector (LAD, >8m2 effective area, 2-30
keV, 240 eV spectral resolution, 1 degree collimated field of view)
and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view,
1 arcmin source location accuracy, 300 eV spectral resolution). The
WFM is equipped with an on-board system for bright events (e.g.,
GRB) localization. The trigger time and position of these events are
broadcast to the ground within 30 s from discovery. In this paper we
present the current technical and programmatic status of the mission.
Title: Preservation of coal-waste geochemical markers in vegetation
and soil on self-heating coal-waste dumps in Silesia, Poland
Authors: Fabiańska, Monika J.; Ciesielczuk, Justyna; Misz-Kennan,
Magdalena; Kruszewski, Łukasz; Kowalski, Adam
Bibcode: 2016ChEG...76..211F
Altcode:
No abstract at ADS
Title: Spectral analysis and modeling of solar flares chromospheric
condensation
Authors: Cauzzi, Gianna; Graham, David; Kowalski, Adam; Zangrilli,
Luca; Simoes, Paulo; Allred, Joel C.
Bibcode: 2016SPD....47.0609C
Altcode:
We follow up on our recent analysis of the X1.1 flare
SOL2014-09-10T17:45, where we studied the impulsive phase dynamics
of tens of individual flaring "kernels", in both coronal (Fe XXI)
and chromospheric (MgII) lines observed at high cadence with IRIS.We
concentrate here on the chromospheric aspect of the phenomenon,
extending the analysis to multiple spectral lines of Mg II, Fe II,
Si I, C II. We show that many flaring kernels display high velocity
downflows in the spectra of all these chromospheric lines, exhibiting
distinct, transient and strongly redshifted spectral components.From
modeling using RADYN with the thick-target interpretation, the presence
of two spectral components appears to be consistent with a high flux
beam of accelerated electrons, characterized by a hard spectrum. In
particular the highest energy electrons heat the denser, lower layers
of the atmosphere, while the bulk of the beam energy, deposited higher
in the atmosphere, is sufficient to produce chromospheric evaporation
with a corresponding condensation.
Title: FUV Continuum in Flare Kernels Observed by IRIS
Authors: Daw, Adrian N.; Kowalski, Adam; Allred, Joel C.; Cauzzi,
Gianna
Bibcode: 2016SPD....47.0604D
Altcode:
Fits to Interface Region Imaging Spectrograph (IRIS) spectra observed
from bright kernels during the impulsive phase of solar flares are
providing long-sought constraints on the UV/white-light continuum
emission. Results of fits of continua plus numerous atomic and molecular
emission lines to IRIS far ultraviolet (FUV) spectra of bright kernels
are presented. Constraints on beam energy and cross sectional area
are provided by cotemporaneous RHESSI, FERMI, ROSA/DST, IRIS slit-jaw
and SDO/AIA observations, allowing for comparison of the observed IRIS
continuum to calculations of non-thermal electron beam heating using
the RADYN radiative-hydrodynamic loop model.
Title: The MUSCLES Treasury Survey. I. Motivation and Overview
Authors: France, Kevin; Loyd, R. O. Parke; Youngblood, Allison;
Brown, Alexander; Schneider, P. Christian; Hawley, Suzanne L.;
Froning, Cynthia S.; Linsky, Jeffrey L.; Roberge, Aki; Buccino,
Andrea P.; Davenport, James R. A.; Fontenla, Juan M.; Kaltenegger,
Lisa; Kowalski, Adam F.; Mauas, Pablo J. D.; Miguel, Yamila; Redfield,
Seth; Rugheimer, Sarah; Tian, Feng; Vieytes, Mariela C.; Walkowicz,
Lucianne M.; Weisenburger, Kolby L.
Bibcode: 2016ApJ...820...89F
Altcode: 2016arXiv160209142F
Ground- and space-based planet searches employing radial velocity
techniques and transit photometry have detected thousands
of planet-hosting stars in the Milky Way. With so many planets
discovered, the next step toward identifying potentially habitable
planets is atmospheric characterization. While the Sun-Earth system
provides a good framework for understanding the atmospheric chemistry
of Earth-like planets around solar-type stars, the observational
and theoretical constraints on the atmospheres of rocky planets in
the habitable zones (HZs) around low-mass stars (K and M dwarfs) are
relatively few. The chemistry of these atmospheres is controlled by the
shape and absolute flux of the stellar spectral energy distribution
(SED), however, flux distributions of relatively inactive low-mass
stars are poorly understood at present. To address this issue, we
have executed a panchromatic (X-ray to mid-IR) study of the SEDs of
11 nearby planet-hosting stars, the Measurements of the Ultraviolet
Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES)
Treasury Survey. The MUSCLES program consists visible observations from
Hubble and ground-based observatories. Infrared and astrophysically
inaccessible wavelengths (EUV and Lyα) are reconstructed using
stellar model spectra to fill in gaps in the observational data. In
this overview and the companion papers describing the MUSCLES survey,
we show that energetic radiation (X-ray and ultraviolet) is present from
magnetically active stellar atmospheres at all times for stars as late
as M6. The emission line luminosities of C IV and Mg II are strongly
correlated with band-integrated luminosities and we present empirical
relations that can be used to estimate broadband FUV and XUV (≡X-ray +
EUV) fluxes from individual stellar emission line measurements. We find
that while the slope of the SED, FUV/NUV, increases by approximately
two orders of magnitude form early K to late M dwarfs (≈0.01-1), the
absolute FUV and XUV flux levels at their corresponding HZ distances
are constant to within factors of a few, spanning the range 10-70 erg
cm-2 s-1 in the HZ. Despite the lack of strong
stellar activity indicators in their optical spectra, several of the
M dwarfs in our sample show spectacular UV flare emission in their
light curves. We present an example with flare/quiescent ultraviolet
flux ratios of the order of 100:1 where the transition region
energy output during the flare is comparable to the total quiescent
luminosity of the star Eflare(UV) ∼ 0.3 L*Δt
(Δt = 1 s). Finally, we interpret enhanced L(line)/LBol
ratios for C IV and N v as tentative observational evidence for the
interaction of planets with large planetary mass-to-orbital distance
ratios (Mplan/aplan) with the transition regions
of their host stars. Based on observations made with the NASA/ESA
Hubble Space Telescope, obtained from the data archive at the Space
Telescope Science Institute. STScI is operated by the Association
of Universities for Research in Astronomy, Inc. under NASA contract
NAS 5-26555.
Title: M Dwarf Flare Continuum Variations on One-second Timescales:
Calibrating and Modeling of ULTRACAM Flare Color Indices
Authors: Kowalski, Adam F.; Mathioudakis, Mihalis; Hawley, Suzanne L.;
Wisniewski, John P.; Dhillon, Vik S.; Marsh, Tom R.; Hilton, Eric J.;
Brown, Benjamin P.
Bibcode: 2016ApJ...820...95K
Altcode: 2016arXiv160204879K
We present a large data set of high-cadence dMe flare light curves
obtained with custom continuum filters on the triple-beam, high-speed
camera system ULTRACAM. The measurements provide constraints for models
of the near-ultraviolet (NUV) and optical continuum spectral evolution
on timescales of ≈1 s. We provide a robust interpretation of the
flare emission in the ULTRACAM filters using simultaneously obtained
low-resolution spectra during two moderate-sized flares in the dM4.5e
star YZ CMi. By avoiding the spectral complexity within the broadband
Johnson filters, the ULTRACAM filters are shown to characterize
bona fide continuum emission in the NUV, blue, and red wavelength
regimes. The NUV/blue flux ratio in flares is equivalent to a Balmer
jump ratio, and the blue/red flux ratio provides an estimate for the
color temperature of the optical continuum emission. We present a new
“color-color” relationship for these continuum flux ratios at the
peaks of the flares. Using the RADYN and RH codes, we interpret the
ULTRACAM filter emission using the dominant emission processes from a
radiative-hydrodynamic flare model with a high nonthermal electron beam
flux, which explains a hot, T ≈ 104 K, color temperature
at blue-to-red optical wavelengths and a small Balmer jump ratio as
observed in moderate-sized and large flares alike. We also discuss the
high time resolution, high signal-to-noise continuum color variations
observed in YZ CMi during a giant flare, which increased the NUV flux
from this star by over a factor of 100. Based on observations
obtained with the Apache Point Observatory 3.5 m telescope, which is
owned and operated by the Astrophysical Research Consortium, based on
observations made with the William Herschel Telescope operated on the
island of La Palma by the Isaac Newton Group in the Spanish Observatorio
del Roque de los Muchachos of the Instituto de Astrofsica de Canarias,
and observations, and based on observations made with the ESO Telescopes
at the La Silla Paranal Observatory under programme ID 085.D-0501(A).
Title: White-light continuum in stellar flares
Authors: Kowalski, Adam F.
Bibcode: 2016IAUS..320..259K
Altcode: 2015arXiv151105085K
In this talk, we discuss the formation of the near-ultraviolet and
optical continuum emission in M dwarf flares through the formation of a
dense, heated chromospheric condensation. Results are used from a recent
radiative-hydrodynamic model of the response of an M dwarf atmosphere
to a high energy flux of nonthermal electrons. These models are used to
infer the charge density and optical depth in continuum emitting flare
layers from spectra covering the Balmer jump and optical wavelength
regimes. Future modeling and observational directions are discussed.
Title: A Very Bright, Very Hot, and Very Long Flaring Event from
the Young Nearby M Dwarf Binary DG CVn
Authors: Osten, Rachel A.; Drake, Stephen Alan; Kowalski, Adam;
Krimm, Hans A.; Page, Kim; Gazeas, Kosmas; Kennea, Jamie A.; Oates,
Sam; Page, Mat; Gehrels, Neil
Bibcode: 2016AAS...22714517O
Altcode:
On April 23, 2014, the Swift satellite responded to a hard X-ray
transient detected by its Burst Alert Telescope, which turned out to be
a stellar flare from a nearby, young M dwarf binary DG~CVn. Observations
at X-ray, UV and optical wavelengths of the main impulsive flare and
subsequent smaller events reveal a complex pattern of flare events
extending over about three weeks. We find that the X-ray spectrum of the
primary outburst can be adequately described by either a single very
high temperature plasma or a nonthermal thick-target bremmstrahlung
model. By evaluating accompanying data of this event and analysis
of a second brightening, we argue that the thermal interpretation is
more likely on energetic grounds. The primary outburst lasted a few
hours and produced the highest temperature thermal plasmas ever seen
spectroscopically over the 0.3-100 keV range in a stellar flare, at
TX of 300 MK. The X-ray luminosity of the main flare exceeded
the bolometric luminosity of the brighter component (LX
>1.6Lbol) for ~360 seconds. The first event was followed
by a comparably energetic event almost a day later, whose coverage
at X-ray and optical wavelengths enables inferences about it and the
first event. In particular we find evidence for stellar radius-sized
coronal loops filled with dense (ne>1012
cm-3) coronal plasma. The radiated energy in X-rays and white
light reveal these first two events to be some of the most energetic
X-ray and white light flares from an M dwarf. These structures require
large coronal magnetic field strengths (a few kG for the first event,
hundreds of Gauss for the second) to confine the plasma, and we thus
predict an extremely high photospheric magnetic field strength of
several kiloGauss.
Title: New Insights into White-Light Flare Emission from
Radiative-Hydrodynamic Modeling of a Chromospheric Condensation
Authors: Kowalski, Adam F.; Hawley, S. L.; Carlsson, M.; Allred,
J. C.; Uitenbroek, H.; Osten, R. A.; Holman, G.
Bibcode: 2015SoPh..290.3487K
Altcode: 2015SoPh..tmp...61K; 2015arXiv150307057K
The heating mechanism at high densities during M-dwarf flares is
poorly understood. Spectra of M-dwarf flares in the optical and
near-ultraviolet wavelength regimes have revealed three continuum
components during the impulsive phase: 1) an energetically dominant
blackbody component with a color temperature of T ≈104K
in the blue-optical, 2) a smaller amount of Balmer continuum emission
in the near-ultraviolet at λ ≤3 646 Å, and 3) an apparent
pseudo-continuum of blended high-order Balmer lines between λ =3
646 Å and λ ≈3 900 Å. These properties are not reproduced by
models that employ a typical "solar-type" flare heating level of
≤1011ergcm−2s−1 in nonthermal
electrons, and therefore our understanding of these spectra is
limited to a phenomenological three-component interpretation. We
present a new 1D radiative-hydrodynamic model of an M-dwarf flare
from precipitating nonthermal electrons with a high energy flux of
1013ergcm−2s−1. The simulation
produces bright near-ultraviolet and optical continuum emission from a
dense (n >1015cm−3), hot (T ≈12 000 -13 500
K) chromospheric condensation. For the first time, the observed color
temperature and Balmer jump ratio are produced self-consistently in a
radiative-hydrodynamic flare model. We find that a T ≈104K
blackbody-like continuum component and a low Balmer jump ratio result
from optically thick Balmer (∞ →n =2 ) and Paschen recombination
(∞ →n =3 ) radiation, and thus the properties of the flux spectrum
are caused by blue (λ ≈4 300 Å) light escaping over a larger
physical depth range than by red (λ ≈6 700 Å) and near-ultraviolet
(λ ≈3 500 Å) light. To model the near-ultraviolet pseudo-continuum
previously attributed to overlapping Balmer lines, we include the
extra Balmer continuum opacity from Landau-Zener transitions that
result from merged, high-order energy levels of hydrogen in a dense,
partially ionized atmosphere. This reveals a new diagnostic of ambient
charge density in the densest regions of the atmosphere that are heated
during dMe and solar flares.
Title: Hα Line Profile Asymmetries and the Chromospheric Flare
Velocity Field
Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van
der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski,
A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P.
Bibcode: 2015ApJ...813..125K
Altcode: 2015arXiv151001877K
The asymmetries observed in the line profiles of solar flares can
provide important diagnostics of the properties and dynamics of the
flaring atmosphere. In this paper the evolution of the Hα and Ca ii
λ8542 lines are studied using high spatial, temporal, and spectral
resolution ground-based observations of an M1.1 flare obtained with
the Swedish 1 m Solar Telescope. The temporal evolution of the Hα
line profiles from the flare kernel shows excess emission in the red
wing (red asymmetry) before flare maximum and excess in the blue wing
(blue asymmetry) after maximum. However, the Ca ii λ8542 line does
not follow the same pattern, showing only a weak red asymmetry during
the flare. RADYN simulations are used to synthesize spectral line
profiles for the flaring atmosphere, and good agreement is found
with the observations. We show that the red asymmetry observed in
Hα is not necessarily associated with plasma downflows, and the blue
asymmetry may not be related to plasma upflows. Indeed, we conclude
that the steep velocity gradients in the flaring chromosphere modify
the wavelength of the central reversal in the Hα line profile. The
shift in the wavelength of maximum opacity to shorter and longer
wavelengths generates the red and blue asymmetries, respectively.
Title: Properties of Flares on GKM Stars in Kepler
Authors: Hawley, Suzanne; Davenport, James R. A.; Hebb, Leslie;
Kowalski, Adam Francis; Wisniewski, John
Bibcode: 2015IAUGA..2253855H
Altcode:
We analyze Kepler observations of G and K stars and determine flare
properties, frequencies and energies from both long and short cadence
data. We compare these with our previous results for M dwarfs and
investigate correlations with rotation, starspot phase, differential
rotation and starspot evolution.
Title: White-light continuum in solar and stellar flares
Authors: Kowalski, Adam Francis
Bibcode: 2015IAUGA..2257997K
Altcode:
During solar and stellar flares, the majority of the radiated energy
from the lower atmosphere escapes as white-light continuum emission in
the near-ultraviolet and optical wavelength regimes. The time-dependent
spectral energy distribution of white-light emission is important
for assessing biomarkers in planetary atmospheres around M dwarfs
and for constraining models of heating at the highest densities in
flares. I will discuss the observational characteristics of white-light
emission from recent spectroscopic observations of M dwarf flares, and
I will describe a new interpretation of these spectra as revealed in a
radiative-hydrodynamic model of an extreme chromospheric condensation. I
will give an overview of the properties of white-light emission in
solar flares and the new information obtained for the brightest solar
flare kernels observed with IRIS.
Title: A Unified Computational Model for Solar and Stellar Flares
Authors: Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats
Bibcode: 2015ApJ...809..104A
Altcode: 2015arXiv150704375A
We present a unified computational framework that can be used to
describe impulsive flares on the Sun and on dMe stars. The models
assume that the flare impulsive phase is caused by a beam of charged
particles that is accelerated in the corona and propagates downward
depositing energy and momentum along the way. This rapidly heats
the lower stellar atmosphere causing it to explosively expand and
dramatically brighten. Our models consist of flux tubes that extend from
the sub-photosphere into the corona. We simulate how flare-accelerated
charged particles propagate down one-dimensional flux tubes and heat the
stellar atmosphere using the Fokker-Planck kinetic theory. Detailed
radiative transfer is included so that model predictions can be
directly compared with observations. The flux of flare-accelerated
particles drives return currents which additionally heat the stellar
atmosphere. These effects are also included in our models. We examine
the impact of the flare-accelerated particle beams on model solar and
dMe stellar atmospheres and perform parameter studies varying the
injected particle energy spectra. We find the atmospheric response
is strongly dependent on the accelerated particle cutoff energy and
spectral index.
Title: A Unified Computational Model for Solar and Stellar Flares
Authors: Allred, Joel; Kowalski, Adam; Carlsson, Mats
Bibcode: 2015TESS....130207A
Altcode:
We describe a unified computational framework which can be used to model
impulsive flares on the Sun and on dMe stars. The models are constructed
assuming that the flare impulsive phase is caused by a beam of charged
particles (primarily electrons and protons) that is accelerated in the
corona and propagates downward depositing energy and momentum along
the way. This rapidly heats the lower stellar atmosphere causing it to
explosively expand and emission to dramatically brighten. Our models
consist of flux tubes that extend from the sub-photosphere into the
corona. We simulate how these flare-accelerated particles propagate
down one dimensional flux tubes and heat the stellar atmosphere
using Fokker-Planck kinetic theory. Detailed radiative transfer is
included so that model predictions can be directly compared with
observations. The flux of flare-accelerated particles drives return
currents which additionally heat the stellar atmosphere, and these
effects are also included in our models. We examine the impact of
the flare-accelerated particle beams on model solar and dMe stellar
atmospheres and perform parameter studies varying the injected particle
energy spectra. We find the atmospheric response is strongly dependent
on the accelerated particle cutoff energy and spectral index.
Title: State-of-the-Art Observations and Modeling of Stellar Flares
Authors: Kowalski, Adam F.; Hawley, Suzanne L.
Bibcode: 2015HiA....16...99K
Altcode:
Flares are observed on a wide variety of stellar types, ranging from
closely orbiting binary systems consisting of an evolved member (RS
CVn's) and young, nearby super-active M dwarfs (dMe's). The timescales
and energies of flares span many orders of magnitude and typically
far exceed the scales of even the largest solar flares observed. In
particular, the active M dwarfs produce an energetic signature in
the near-UV and optical continuum, which is often referred to as
the white-light continuum. White-light emission has been studied in
Johnson UBVR filters during a few large-amplitude flares, and the best
emission mechanism that fits the broadband color distribution is a
T~104 K blackbody (Hawley & Fisher 1992). Time-resolved
blue spectra have revealed a consistent picture, with little or
no Balmer jump and a smoothly rising continuum toward the near-UV
(Hawley & Pettersen 1991). However, the most recent self-consistent
radiative-hydrodynamic (RHD) models, which use a solar-type flare
heating function from accelerated, nonthermal electrons, do not
reproduce this emission spectrum. Instead, these models predict that
the white-light is dominated by Balmer continuum emission from Hydrogen
recombination in the chromosphere (Allred et al. 2006). Moreover, Allred
et al. (2006) showed that the Johnson colors of the model prediction
exhibit a broadband distribution similar to a blackbody with T~9000 K.
Title: Serendipitous Discovery of a Dwarf Nova in the Kepler Field
Near the G Dwarf KIC 5438845
Authors: Brown, Alexander; Neff, James E.; Ayres, Thomas R.; Kowalski,
Adam; Hawley, Suzanne; Berdyugina, Svetlana; Harper, Graham M.;
Korhonen, Heidi; Piskunov, Nikolai; Saar, Steven; Walkowicz, Lucianne;
Wells, Mark A.
Bibcode: 2015AJ....149...67B
Altcode:
The Kepler satellite provides a unique window into stellar temporal
variability by observing a wide variety of stars with multi-year,
near-continuous, high precision, optical photometric time series. While
most Kepler targets are faint stars with poorly known physical
properties, many unexpected discoveries should result from a long
photometric survey of such a large area of sky. During our Kepler
Guest Observer programs that monitored late-type stars for starspot and
flaring variability, we discovered a previously unknown dwarf nova that
lies within a few arcseconds of the mid-G dwarf star KIC 5438845. This
dwarf nova underwent nine outbursts over a 4 year time span. The two
largest outbursts lasted ∼17-18 days and show strong modulations with
a 110.8 minute period and a declining amplitude during the outburst
decay phase. These properties are characteristic of an SU UMa-type
cataclysmic variable. By analogy with other dwarf nova light curves,
we associate the 110.8 minute (1.847 hr) period with the superhump
period, close to but slightly longer than the orbital period of the
binary. No precursor outbursts are seen before the super-outbursts
and the overall super-outburst morphology corresponds to Osaki &
Meyer “Case B” outbursts, which are initiated when the outer edge
of the disk reaches the tidal truncation radius. “Case B” outbursts
are rare within the Kepler light curves of dwarf novae. The dwarf nova
is undergoing relatively slow mass transfer, as evidenced by the long
intervals between outbursts, but the mass transfer rate appears to
be steady, because the smaller “normal” outbursts show a strong
correlation between the integrated outburst energy and the elapsed time
since the previous outburst. At super-outburst maximum the system was
at V ∼ 18, but in quiescence it is fainter than V ∼ 22, which will
make any detailed quiescent follow-up of this system difficult.
Title: Kepler Flares III: Stellar Activity on GJ 1245A and B
Authors: Lurie, John C.; Davenport, James R. A.; Hawley, Suzanne L.;
Wilkinson, Tessa D.; Wisniewski, John P.; Kowalski, Adam F.; Hebb,
Leslie
Bibcode: 2015ApJ...800...95L
Altcode: 2014arXiv1412.6109L
We present the flare occurrence rates and starspot evolution for GJ
1245A and B, two active M5 stars, based on nine months of Kepler short
cadence observations, and four years of nearly continuous long cadence
observations. The A component is separated from the B component by 7'',
and the stars are not resolved in the Kepler pipeline processing due
to Kepler's large plate scale of 4'' pixel-1. Analyzing
the target pixel data, we have generated separate light curves for
components A and B using the PyKE pixel response function modeling
procedures, and note the effects of CCD saturation and nonlinear
response to high-energy flares. In our sample, GJ 1245A and B exhibit
an average of 3.0 and 2.6 flares per day, respectively. We introduce
a new metric, Lfl /L Kp, to compare the flare
rates between stars, and discuss this in the context of GJ 1245A and
B. Both stars exhibit starspot features that evolve on long timescales,
with the slower rotating B component showing evidence of differential
rotation. Intriguingly, the angular separation between the A and B
component photocenters decreases during the four years of observations
in a manner consistent with a shift in the position of the A photocenter
due to the orbit of its unseen M8 companion (GJ 1245C), which is ~94%
less bright. Among the most detailed photometric studies of fully
convective M dwarfs in a multiple system, these results provide an
important constraint on stellar age-rotation-activity models.
Title: Time-Resolved Near-Ultraviolet Flare Spectra with the Hubble
Space Telescope / Cosmic Origins Spectrograph
Authors: Kowalski, Adam F.; Hawley, Suzanne L.; Johns-Krull,
Christopher M.; Schmidt, Sarah J.; Brown, Alexander; Wisniewski, John
P.; Davenport, James R. A.; Farina, Cecilia; Pietro Gentile Fusillo,
Nicola; Xilouris, Manolis; Mathioudakis, Mihalis; Osten, Rachel A.;
Holtzman, Jon A.; Phan-Bao, Ngoc; Valenti, Jeff A.; Walkowicz, Lucianne
Bibcode: 2015AAS...22544903K
Altcode:
A large amount of the radiated energy during solar and stellar flares
is emitted as white-light continuum emission, extending through the
ultraviolet and optical wavelength regimes. Broadband photometry
and optical spectral observations of M dwarf flares suggest that the
white-light peak is located in the near-ultraviolet wavelength regime
similar to a blackbody with T ~ 10,000 K, whereas radiative-hydrodynamic
models using a solar-type flare heating mechanism (nonthermal electrons
with a flux ~ 1011 erg / s / cm2 accelerated in
the corona) predict that the peak lies at redder wavelengths at the
head of the Balmer continuum. We have completed a successful flare
monitoring campaign on the dM4e star GJ 1243, in order to constrain
the time-evolution of the peak of the white-light continuum. The
campaign took place over 12 hours on Aug 31/Sept 1, 2014, and included
optical monitoring from nine ground-based telescopes as the Hubble
Space Telescope recorded time-tagged spectra in the near-ultraviolet
(2450-2840 Å) with the Cosmic Origins Spectrograph. Two flares occurred
during the HST observations, and we show preliminary results relating
the continuum and line (Fe II and Mg II) emission to the simultaneous
ground-based optical spectra and photometry. This dataset provides new
constraints for radiative-hydrodynamic modeling of the lower flaring
atmosphere in addition to input for models of the effects of flares
on biomarkers and habitability around M dwarfs.
Title: Optical Spectral Observations of a Flickering White-light
Kernel in a C1 Solar Flare
Authors: Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay
Bibcode: 2015ApJ...798..107K
Altcode: 2014arXiv1411.0770K
We analyze optical spectra of a two-ribbon, long-duration
C1.1 flare that occurred on 2011 August 18 within AR 11271
(SOL2011-08-18T15:15). The impulsive phase of the flare was observed
with a comprehensive set of space-borne and ground-based instruments,
which provide a range of unique diagnostics of the lower flaring
atmosphere. Here we report the detection of enhanced continuum emission,
observed in low-resolution spectra from 3600 Å to 4550 Å acquired
with the Horizontal Spectrograph at the Dunn Solar Telescope. A small,
<=0.''5 (1015 cm2) penumbral/umbral kernel
brightens repeatedly in the optical continuum and chromospheric
emission lines, similar to the temporal characteristics of the hard
X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi
spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal
electron beam energy flux high enough to produce the optical contrast
in our flare spectra would predict a large Balmer jump in emission,
indicative of hydrogen recombination radiation from the upper flare
chromosphere. However, we find no evidence of such a Balmer jump in
the bluemost spectral region of the continuum excess. Just redward of
the expected Balmer jump, we find evidence of a "blue continuum bump"
in the excess emission which may be indicative of the merging of the
higher order Balmer lines. The large number of observational constraints
provides a springboard for modeling the blue/optical emission for this
particular flare with radiative-hydrodynamic codes, which are necessary
to understand the opacity effects for the continuum and emission line
radiation at these wavelengths.
Title: The Continued Optical to Mid-Infrared Evolution of V838
Monocerotis
Authors: Loebman, S. R.; Wisniewski, J. P.; Schmidt, S. J.; Kowalski,
A. F.; Barry, R. K.; Bjorkman, K. S.; Hammel, H. B.; Hawley, S. L.;
Hebb, L.; Kasliwal, M. M.; Lynch, D. K.; Russell, R. W.; Sitko, M. L.;
Szkody, P.
Bibcode: 2015AJ....149...17L
Altcode: 2014arXiv1409.2513L
The eruptive variable V838 Monocerotis (V838 Mon) gained notoriety in
2002 when it brightened nine magnitudes in a series of three outbursts
and then rapidly evolved into an extremely cool supergiant. We
present optical, near-infrared (near-IR), and mid-IR spectroscopic
and photometric observations of V838 Mon obtained between 2008 and
2012 at the Apache Point Observatory 3.5 m, NASA IRTF 3 m, and Gemini
South 8 m telescopes. We contemporaneously analyze the optical and IR
spectroscopic properties of V838 Mon to arrive at a revised spectral
type L3 supergiant and effective temperature {{T}eff}∼
2000-2200 K. Because there are no existing optical observational
data for L supergiants, we speculate that V838 Mon may represent
the prototype for L supergiants in this wavelength regime. We find
a low level of Hα emission present in the system, consistent with
interaction between V838 Mon and its B3V binary; however, we cannot
rule out a stellar collision as the genesis event, which could result
in the observed Hα activity. Based upon a two-component blackbody
fit to all wavelengths of our data, we conclude that, as of 2009,
a shell of ejecta surrounded V838 Mon at a radius of R=263+/- 10 AU
with a temperature of T=285+/- 2 K. This result is consistent with
IR interferometric observations from the same era and predictions
from the Lynch et al. model of the expanding system, which provides a
simple framework for understanding this complicated system. This
publication is partially based on observations obtained with the Apache
Point Observatory 3.5 m telescope, which is owned and operated by the
Astrophysical Research Consortium.
Title: Stellar flares observed by LOFT: implications for the physics
of coronae and for the "space weather" environment of extrasolar
planets
Authors: Drake, S. A.; Behar, E.; Doyle, J. G.; Güdel, M.; Hamaguchi,
K.; Kowalski, A. F.; Maccarone, T.; Osten, R. A.; Peretz, U.; Wolk,
S. J.
Bibcode: 2015arXiv150102771D
Altcode:
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA
mission. We discuss the potential of LOFT for the study of stellar
flares. For a summary, we refer to the paper.
Title: Upgrading the Solar-Stellar Connection: News about activity
in Cool Stars
Authors: Gunther, H. M.; Poppenhaeger, K.; Testa, P.; Borgniet, S.;
Brun, A. S.; Cegla, H. M.; Garraffo, C.; Kowalski, A.; Shapiro, A.;
Shkolnik, E.; Spada, F.; Vidotto, A. A.
Bibcode: 2015csss...18...25G
Altcode: 2014arXiv1408.3068G
In this splinter session, ten speakers presented results on solar
and stellar activity and how the two fields are connected. This was
followed by a lively discussion and supplemented by short, one-minute
highlight talks. The talks presented new theoretical and observational
results on mass accretion on the Sun, the activity rate of flare stars,
the evolution of the stellar magnetic field on time scales of a single
cycle and over the lifetime of a star, and two different approaches
to model the radial-velocity jitter in cool stars that is due to the
granulation on the surface. Talks and discussion showed how much the
interpretation of stellar activity data relies on the sun and how the
large number of objects available in stellar studies can extend the
parameter range of activity models.
Title: Kepler Flares. II. The Temporal Morphology of White-light
Flares on GJ 1243
Authors: Davenport, James R. A.; Hawley, Suzanne L.; Hebb, Leslie;
Wisniewski, John P.; Kowalski, Adam F.; Johnson, Emily C.; Malatesta,
Michael; Peraza, Jesus; Keil, Marcus; Silverberg, Steven M.; Jansen,
Tiffany C.; Scheffler, Matthew S.; Berdis, Jodi R.; Larsen, Daniel M.;
Hilton, Eric J.
Bibcode: 2014ApJ...797..122D
Altcode: 2014arXiv1411.3723D
We present the largest sample of flares ever compiled for a single M
dwarf, the active M4 star GJ 1243. Over 6100 individual flare events,
with energies ranging from 1029 to 1033 erg, are
found in 11 months of 1 minute cadence data from Kepler. This sample
is unique for its completeness and dynamic range. We have developed
automated tools for finding flares in short-cadence Kepler light curves,
and performed extensive validation and classification of the sample by
eye. From this pristine sample of flares we generate a median flare
template. This template shows that two exponential cooling phases
are present during the white-light flare decay, providing fundamental
constraints for models of flare physics. The template is also used as
a basis function to decompose complex multi-peaked flares, allowing us
to study the energy distribution of these events. Only a small number
of flare events are not well fit by our template. We find that complex,
multi-peaked flares occur in over 80% of flares with a duration of 50
minutes or greater. The underlying distribution of flare durations for
events 10 minutes and longer appears to follow a broken power law. Our
results support the idea that sympathetic flaring may be responsible
for some complex flare events.
Title: Kepler Flares. I. Active and Inactive M Dwarfs
Authors: Hawley, Suzanne L.; Davenport, James R. A.; Kowalski, Adam F.;
Wisniewski, John P.; Hebb, Leslie; Deitrick, Russell; Hilton, Eric J.
Bibcode: 2014ApJ...797..121H
Altcode: 2014arXiv1410.7779H
We analyzed Kepler short-cadence M dwarf observations. Spectra from the
Astrophysical Research Consortium 3.5 m telescope identify magnetically
active (Hα in emission) stars. The active stars are of mid-M spectral
type, have numerous flares, and have well-defined rotational modulation
due to starspots. The inactive stars are of early M type, exhibit less
starspot signature, and have fewer flares. A Kepler to U-band energy
scaling allows comparison of the Kepler flare frequency distributions
with previous ground-based data. M dwarfs span a large range of flare
frequency and energy, blurring the distinction between active and
inactive stars designated solely by the presence of Hα. We analyzed
classical and complex (multiple peak) flares on GJ 1243, finding strong
correlations between flare energy, amplitude, duration, and decay time,
with only a weak dependence on rise time. Complex flares last longer and
have higher energy at the same amplitude, and higher energy flares are
more likely to be complex. A power law fits the energy distribution for
flares with log EK_p \gt 31 erg, but the predicted number of
low-energy flares far exceeds the number observed, at energies where
flares are still easily detectable, indicating that the power-law
distribution may flatten at low energy. There is no correlation of
flare occurrence or energy with starspot phase, the flare waiting
time distribution is consistent with flares occurring randomly in
time, and the energies of consecutive flares are uncorrelated. These
observations support a scenario where many independent active regions
on the stellar surface are contributing to the observed flare rate.
Title: Continuum Emission from a Microflare Kernel Observed by IRIS
Authors: Daw, A. N.; Kowalski, A. F.; Wuelser, J. P.; Cauzzi, G.;
Allred, J. C.; Christe, S.
Bibcode: 2014AGUFMSH51C4166D
Altcode:
Fits to Interface Region Imaging Spectrograph (IRIS) spectra observed
from a bright kernel during the impulsive phase of a solar microflare
(GOES class B9) are presented, providing long-sought constraints on
the UV/white-light continuum emission during flares. Constraints on
beam energy and cross sectional area are provided by cotemporaneous
RHESSI and SDO/AIA 1700 A observations, respectively, allowing for
comparison of the observed IRIS continuum to calculations of non-thermal
electron beam heating using the RADYN radiative-hydrodynamic loop
model. Implications for flare energy release are discussed.
Title: Very Bright, Very Hot and Very Long: Swift Observations of
the DG CVn "Superflare" of April 23rd, 2014
Authors: Drake, Stephen Alan; Osten, Rachel A.; Page, Kim L; Kennea,
Jamie A; Oates, Samantha R; Krimm, Hans A; Gehrels, Neil; Page,
Mathew J; Kowalski, Adam
Bibcode: 2014HEAD...1440406D
Altcode:
On April 23rd this year, one of the 2 stars in the close visual binary
dM4e system DG CVn flared to a level bright enough 300 milliCrab in the
15-150 keV band) that it triggered the Swift Burst Alert Telescope. Two
minutes later, after Swift had slewed to the direction of this source,
the Swift X-ray Telescope (XRT) and the Ultraviolet Optical Telescope
(UVOT) commenced observing this flare. These observations continued
(intermittently) for about 20 days and yielded a fascinating case
history of this colossal event, the decay of which took more than a
week in the UV and soft X-ray regions, and included several smaller
superimposed secondary flares. The peak 0.3-10 keV luminosity observed
by the XRT of 1.9e32 erg/s at the 18 pc distance of this system is
1.5 times the 'normal' combined systemic bolometric luminosity of
1.3e32 erg/s, making this event a super-bolometric flare similar
to the 2008 flare of EV Lac (also detected by Swift). The BAT and
XRT spectra of this flare in the first 6 minutes indicate that the
emission was dominated by very hot (>>10 keV) plasma and/or a
non-thermal power-law emission. This flare is arguably the longest,
most X-ray luminous and hottest flare ever seen for an M dwarf in the
solar neighborhood, and is reminiscent of the 9 days long flare of the
RS CVn binary CF Tuc detected by ROSAT. We discuss how these exceptional
characteristics may be related to the known properties of this system,
specifically to its youth (30 Myr) and rapid rotation (55 km/s).
Title: Characterizing NUV Flare Radiation from M Dwarfs
Authors: Kowalski, Adam
Bibcode: 2014koa..prop..432K
Altcode:
We seek to locate the peak of the white-light continuum during an M
dwarf flare using combined data from HST and Keck. The observations will
be critical for constraining radiative-hydrodynamic flare models that
use a solar-type heating function and for simulations of habitability
around M dwarfs.
Title: The Atmospheric Response to High Fluxes of Nonthermal Electrons
during M Dwarf Flares
Authors: Kowalski, Adam; Allred, J. C.; Carlsson, M.; Hawley, S. L.;
Holman, G. D.; Mathioudakis, M.; Osten, R. A.; Uitenbroek, H.
Bibcode: 2014AAS...22315117K
Altcode:
Flares are thought to be the result of magnetic fields in the stellar
corona that undergo reconnection and accelerate charged particles
into the lower atmosphere. Spectra of M dwarf flares in the optical
and near-ultraviolet wavelength regimes can be used to constrain the
heating mechanism of the lower stellar atmosphere. These observations
show several ubiquitous properties of the continuum emission, which
is not reproduced by models that use typical “solar-type” heating
functions. We present results from a grid of new flare models using the
RADYN code, which simultaneously calculates the radiative transfer and
hydrodynamics on short timescales. We explore the atmospheric response
to a short ~2 second burst of a very high heating rate from nonthermal
electrons using a solar-type heating function, and we propose a new
“M dwarf-type” heating variation that explains a range of observed
spectral properties, such as ~10,000 K blackbody emission and a smooth
continuum across the Balmer jump wavelength (3646A).
Title: Hot-Wiring Flare Stars: Optical Flare Rates and Properties
from Time-Domain Surveys
Authors: Kowalski, A.
Bibcode: 2014htu..conf...15K
Altcode:
Flares are thought to result from the reconnection of magnetic fields in
the upper layers (coronae) of stellar atmospheres. The highly dynamic
atmospheric response produces radiation across the electromagnetic
spectrum, from the radio to X-rays, on a range of timescales, from
seconds to days. Due to their high flare rates and energies combined
with a large contrast against the background quiescent emission, the
low-mass M dwarfs are the primary target for studying flare rates in the
Galaxy. However, high-precision monitoring campaigns using Kepler and
the Hubble Space Telescope have recently revealed important information
on the flare rates of earlier- type, more massive stars. In this talk,
I will focus on the properties of flares and flare stars in the optical
and near-ultraviolet wavelength regimes as revealed from time-domain
surveys, such as the repeat observations of the Sloan Digital Sky
Surveys Stripe 82. I will discuss the importance of spectroscopic
follow-up characterization of the quiescent and flare emission, and I
will highlight new radiative-hydrodynamic modeling results that have
enhanced our understanding of impulsive phase U-band flare emission.
Title: Taking the Temperature of Explosive Stellar Flares
Authors: Kowalski, Adam
Bibcode: 2013hst..prop13323K
Altcode:
State-of-the-art radiative hydrodynamic models which employ solar
flare heating mechanisms are not able to produce a key observational
component of stellar flares, hot blackbody emission, indicating that
there is significant physics missing from our understanding of energy
transport and radiation during stellar flares. Efforts to resolve this
discrepancy using blue-optical spectrophotometry have proven to be
insufficient to accurately constrain the temperature of this blackbody
emission and more generally the depth in the atmosphere at which this
emission originates. We propose to rectify this shortcoming by using
HST/COS to measure the flare blackbody temperatures on the active
dM4e star GJ 1243, a star whose frequency of moderate-size flares is
extremely well characterized thanks to our Kepler GO-2/3 programs.
Title: The Decaying Long-period Oscillation of a Stellar Megaflare
Authors: Anfinogentov, S.; Nakariakov, V. M.; Mathioudakis, M.;
Van Doorsselaere, T.; Kowalski, A. F.
Bibcode: 2013ApJ...773..156A
Altcode:
We analyze and interpret the oscillatory signal in the decay phase of
the U-band light curve of a stellar megaflare observed on 2009 January
16 on the dM4.5e star YZ CMi. The oscillation is well approximated
by an exponentially decaying harmonic function. The period of the
oscillation is found to be 32 minutes, the decay time about 46 minutes,
and the relative amplitude 15%. As this observational signature is
typical of the longitudinal oscillations observed in solar flares at
extreme ultraviolet and radio wavelengths, associated with standing
slow magnetoacoustic waves, we suggest that this megaflare may be of a
similar nature. In this scenario, macroscopic variations of the plasma
parameters in the oscillations modulate the ejection of non-thermal
electrons. The phase speed of the longitudinal (slow magnetoacoustic)
waves in the flaring loop or arcade, the tube speed, of about 230
km s-1 would require a loop length of about 200 Mm. Other
mechanisms, such as standing kink oscillations, are also considered.
Title: The properties of flare kernels observed by the Dunn Solar
Telescope
Authors: Fletcher, Lyndsay; Kowalski, A.; Cauzzi, G.; Hawley, S. L.;
Hudson, H. S.
Bibcode: 2013SPD....44...67F
Altcode:
We report on a campaign at the Dunn Solar Telescope which resulted in
successful imaging and spectroscopic observations of a C1.1 solar flare
on 18th August 2011. This flare exhibited ribbons with complicated
fine structure at the resolution of the DST/IBIS instrument, and a
number of bright kernels with sizes comparable to the smallest scales
sampled by IBIS, around 2-4 pixels (0."3-0."6) FWHM. We focus on these
bright kernels, describing their spatial characteristics in the core
and wing of H alpha and Ca II 8542, and in the UV and EUV with SDO. We
also show preliminary broad-band spectroscopy of the kernels which may
demonstrate the presence of an optical continuum in this small flare.
Title: Time-resolved Properties and Global Trends in dMe Flares from
Simultaneous Photometry and Spectra
Authors: Kowalski, Adam F.; Hawley, Suzanne L.; Wisniewski, John P.;
Osten, Rachel A.; Hilton, Eric J.; Holtzman, Jon A.; Schmidt, Sarah
J.; Davenport, James R. A.
Bibcode: 2013ApJS..207...15K
Altcode: 2013arXiv1307.2099K
We present a homogeneous analysis of line and continuum emission
from simultaneous high-cadence spectra and photometry covering
near-ultraviolet and optical wavelengths for 20 M dwarf flares. These
data were obtained to study the white-light continuum components at
bluer and redder wavelengths than the Balmer jump. Our goals were
to break the degeneracy between emission mechanisms that have been
fit to broadband colors of flares and to provide constraints for
radiative-hydrodynamic (RHD) flare models that seek to reproduce the
white-light flare emission. The main results from the analysis are
the following: (1) the detection of Balmer continuum (in emission)
that is present during all flares and with a wide range of relative
contributions to the continuum flux at bluer wavelengths than the
Balmer jump; (2) a blue continuum at flare maximum that is linearly
decreasing with wavelength from λ = 4000-4800 Å, indicative of hot,
blackbody emission with typical temperatures of T BB
~ 9000-14, 000 K (3) a redder continuum apparent at wavelengths
longer than Hβ (λ >~ 4900 Å) which becomes relatively more
important to the energy budget during the late gradual phase. The hot
blackbody component and redder continuum component have been detected
in previous studies of flares. However, we have found that although
the hot blackbody emission component is relatively well-represented
by a featureless, single-temperature Planck function, this component
includes absorption features and has a continuum shape strikingly
similar to the spectrum of an A-type star as directly observed in
our flare spectra. New model constraints are presented for the time
evolution among the hydrogen Balmer lines and between Ca II K and the
blackbody continuum emission. We calculate Balmer jump flux ratios and
compare to the solar-type flare heating predictions from RHD models. The
model ratios are too large and the blue-optical (λ = 4000-4800 Å)
slopes are too red in both the impulsive and gradual decay phases of
all 20 flares. This discrepancy implies that further work is needed
to understand the heating at high column mass during dMe flares. Based on observations obtained with the Apache Point Observatory
3.5 m telescope, which is owned and operated by the Astrophysical
Research Consortium.
Title: VizieR Online Data Catalog: M dwarf flare spectra (Kowalski+,
2013)
Authors: Kowalski, A. F.; Hawley, S. L.; Wisniewski, J. P.; Osten,
R. A.; Hilton, E. J.; Holtzman, J. A.; Schmidt, S. J.; Davenport,
J. R. A.
Bibcode: 2013yCat..22070015K
Altcode:
The spectral data are contained in FITS files (to be read into IDL with
mrdfits.pro), and the photometry data are contained in two column .dat
files. Spectra were obtained with the Dual-Imaging Spectrograph
(DIS) on the ARC 3.5m telescope at the Apache Point Observatory (APO)
in low-resolution. The observing log for each target star is given in
Table 2. (5 data files).
Title: Failed filament eruption inside a coronal mass ejection in
active region 11121
Authors: Kuridze, D.; Mathioudakis, M.; Kowalski, A. F.; Keys, P. H.;
Jess, D. B.; Balasubramaniam, K. S.; Keenan, F. P.
Bibcode: 2013A&A...552A..55K
Altcode: 2013arXiv1302.5931K
Aims: We study the formation and evolution of a failed filament
eruption observed in NOAA active region 11121 near the southeast limb on
November 6, 2010.
Methods: We used a time series of SDO/AIA 304,
171, 131, 193, 335, and 94 Å images, SDO/HMI magnetograms, as well as
ROSA and ISOON Hα images to study the erupting active region.
Results: We identify coronal loop arcades associated with a quadrupolar
magnetic configuration, and show that the expansion and cancellation
of the central loop arcade system over the filament is followed by
the eruption of the filament. The erupting filament reveals a clear
helical twist and develops the same sign of writhe in the form of
inverse γ-shape.
Conclusions: The observations support the
"magnetic breakout" process in which the eruption is triggered by
quadrupolar reconnection in the corona. We propose that the formation
mechanism of the inverse γ-shape flux rope is the magnetohydrodynamic
helical kink instability. The eruption has failed because of the
large-scale, closed, overlying magnetic loop arcade that encloses
the active region. Movies are available in electronic form at
http://www.aanda.org
Title: MMT Hectochelle Spectral Variability of Active Late-type
Stars in the Kepler Field (2013A)
Authors: Brown, Alexander; Walkowicz, Lucianne; Saar, Steven; Hawley,
Suzanne; Kowalski, Adam; Furesz, Gabor; Piskunov, Nikolai
Bibcode: 2013noao.prop..286B
Altcode:
We have on-going it Kepler photometric monitoring of over 300 active
late-type (mid-A - K) stars as part of our Cycles 1/2/3/4 Guest
Observer (GO) programs with the aim of studying starspot evolution,
differential rotation, activity cycles, and flares. We propose to
use the MMT Hectochelle multiobject spectrograph to observe over
140 of these stars to determine a range of basic physical properties
for the stars, such as radial velocity variations due to binarity,
chromospheric activity levels from Ca II H+K and H(alpha), projected
rotational velocities for comparison to the rotational periods
measured directly by it Kepler, age/youth as indicated by Li I, and
better effective temperature and luminosity estimates. In addition,
to provide a superior sample for statistical studies another 800 GKM
dwarf stars showing either starspot modulation from the it Kepler
Team's data or from our deep XMM X-ray survey will be observed using
the unassigned fibers in each field. These measurements require the
32,000 spectral resolution provided by Hectochelle, which is hard to
obtain efficiently for 13-15th magnitude stars any other way.
Title: Non-thermal processes in coronae and beyond
Authors: Poppenhaeger, K.; Günther, H. M.; Beiersdorfer, P.;
Brickhouse, N. S.; Carter, J. A.; Hudson, H. S.; Kowalski, A.; Lalitha,
S.; Miceli, M.; Wolk, S. J.
Bibcode: 2013AN....334..101P
Altcode: 2013csss...17..101P; 2012arXiv1210.2960P
This contribution summarizes the splinter session ``Non-thermal
processes in coronae and beyond'' held at the Cool Stars 17 workshop
in Barcelona in 2012. It covers new developments in high energy
non-thermal effects in the Earth's exosphere, solar and stellar flares,
the diffuse emission in star forming regions and reviews the state
and the challenges of the underlying atomic databases.
Title: A Large Sample of Magnetically-Active Stars Observed With
Kepler
Authors: Wells, Mark; Neff, J. E.; Brown, A.; Ayres, T. R.; Basri,
G. S.; Berdyugina, S.; Harper, G.; Hawley, S. L.; Korhonen, H.;
Kowalski, A.; Micela, G.; Piskunov, N. E.; Ramsey, L. W.; Saar, S. H.;
Walkowicz, L. M.
Bibcode: 2013AAS...22135415W
Altcode:
We have observed about 325 stars in our Kepler Guest Observer
programs (Cycles 1 through 4). For most of these targets, we are
analyzing extremely high-precision light curves that have been
continuously sampled every 30 minutes for up to 3 years. Our sample
of candidate magnetically-active stars was selected primarily using
GALEX colors. Starspots, pulsations, and variations due to eclipsing
and contact binaries combine to produce a rich variety of light
curves. We have developed semi-automated procedures to characterize
this variability and thus to classify the targets and identify the
physical mechanisms that dominate their Kepler light curves. We will
describe these procedures and discuss the range of physical properties
covered by our final classification scheme. We are using this Kepler
database of variability over timescales of minutes to years to provide
diagnostics of flares, starspot formation, evolution, migration, and
ultimately of stellar cycles in general. This work contains results
obtained using the NASA Kepler satellite and from the Apache Point
Observatory, the MMT (using NOAO community access time), and the
Hobby-Eberly Telescope. Funding is provided by NASA Kepler grants
NNX10AC51G, NNX11AC79G, and NNX12AC85G to the University of Colorado,
by NSF grant AST-1109695 to the College of Charleston, and by a grant
from the South Carolina Space Grant consortium.
Title: Time-resolved properties and global trends in dMe flares from
simultaneous photometry and spectra
Authors: Kowalski, Adam Francis
Bibcode: 2013PhDT.......670K
Altcode:
No abstract at ADS
Title: Young Star Populations in the Kepler Field
Authors: Brown, Alexander; Neff, J. E.; Wells, M.; Saar, S.; Furesz,
G.; Walkowicz, L. M.; Ayres, T. R.; Basri, G. S.; Berdyugina, S.;
Harper, G.; Hawley, S. L.; Korhonen, H.; Kowalski, A.; Micela, G.;
Piskunov, N. E.; Ramsey, L. W.
Bibcode: 2013AAS...22135414B
Altcode:
The Kepler satellite is providing spectacular optical photometric
light-curves of unprecedented precision and duration that routinely
allow detailed studies of stellar magnetic activity on late-type stars
that were difficult previously. Kepler provides multi-year duration
light-curves that allow investigation of how activity phenomena --
such as the growth, migration, and decay of star-spots, differential
rotation, activity cycles, and flaring -- operate on a wide variety of
single and binary stars. The 105 square degree Kepler Field contains
tens of thousands of late-type stars showing rotational modulation due
to star-spots with periods ranging from one day to a ``solar-like''
month. Short rotation periods and high levels of magnetic activity are
strongly correlated. However, there are only two basic reasons why stars
with rotation periods of a few days possess such high angular momentum
--- either they are close binaries or they are young stars. During
Kepler GO Cycles 1 through 4 we have been studying the Long-cadence
(30 minute sampling) photometry of hundreds of active late-type stars
and as an absolutely essential complement we have been obtaining high
resolution optical spectra to understand the physical properties of
these stars. We present results from a spectroscopic survey using the
MMT Hectochelle multi-object echelle of 4 square degrees of the Kepler
Field. We have discovered a significant population of young stars with
Li I absorption indicating ages of ~100 Myr or less at a spatial density
of at least 20 stars per square degree. Our detected young star sample
comprises at least 80 stars and represents a dramatic advance compared
to the previously known sample over the full Kepler Field of three
stars in this age range. Roughly one sixth of the stars observed are
young and a similar number short-period binaries based on 2-4 radial
velocities. We show how the rotational properties of the stars and their
physical properties are related. This work is based on data obtained
with the NASA Kepler satellite and the MMT Hectochelle spectrograph
using NOAO community access time. Support by NASA Kepler grants to the
University of Colorado and by NSF grant to the College of Charleston.
Title: DRAFTS: A Deep, Rapid Archival Flare Transient Search in the
Galactic Bulge
Authors: Osten, Rachel A.; Kowalski, Adam; Sahu, Kailash; Hawley,
Suzanne L.
Bibcode: 2012ApJ...754....4O
Altcode: 2012arXiv1205.1485O
We utilize the Sagittarius Window Eclipsing Extrasolar Planet Search
Hubble Space Telescope/Advanced Camera for Surveys data set for a Deep
Rapid Archival Flare Transient Search to constrain the flare rate toward
the older stellar population in the Galactic bulge. During seven days
of monitoring 229,293 stars brighter than V = 29.5, we find evidence for
flaring activity in 105 stars between V = 20 and V = 28. We divided the
sample into non-variable stars and variable stars whose light curves
contain large-scale variability. The flare rate on variable stars is
~700 times that of non-variable stars, with a significant correlation
between the amount of underlying stellar variability and peak flare
amplitude. The flare energy loss rates are generally higher than
those of nearby well-studied single dMe flare stars. The distribution
of proper motions is consistent with the flaring stars being at the
distance and age of the Galactic bulge. If they are single dwarfs,
then they span a range of ≈1.0-0.25 M ⊙. A majority of
the flaring stars exhibit periodic photometric modulations with P <
3 days. If these are tidally locked magnetically active binary systems,
then their fraction in the bulge is enhanced by a factor of ~20 compared
to the local value. These stars may be useful for placing constraints
on the angular momentum evolution of cool close binary stars. Our
results expand the type of stars studied for flares in the optical
band, and suggest that future sensitive optical time-domain studies
will have to contend with a larger sample of flaring stars than the
M dwarf flare stars usually considered.
Title: MOST Observations of the Flare Star AD Leo
Authors: Hunt-Walker, Nicholas M.; Hilton, Eric J.; Kowalski, Adam F.;
Hawley, Suzanne L.; Matthews, Jaymie M.
Bibcode: 2012PASP..124..545H
Altcode: 2012arXiv1206.5019H
We present continuous, high-precision photometric monitoring data
with 1 minute cadence of the dM3e flare star AD Leo with the MOST
satellite. We observed 19 flares in 5.8 days and found a flare
frequency distribution that is similar to previous studies. The light
curve reveals a sinusoidal modulation with a period of days that we
attribute to the rotation of a stellar spot rotating into and out
of view. We see no correlation between the occurrence of flares and
rotational phase, indicating that there may be many spots distributed
at different longitudes or, possibly, that the modulation is caused
by varying surface coverage of a large polar spot that is viewed
nearly pole-on. The data show no correlation between flare energy
and the time since the previous flare. We use these results to reject
a simple model in which all magnetic energy is stored in one active
region and released only during flares. Based on observations
obtained with the Apache Point Observatory 3.5 m telescope, which is
owned and operated by the Astrophysical Research Consortium.
Title: Solar Flare Observations of the EUV Continua
Authors: Milligan, Ryan O.; Chamberlin, P.; Hudson, H.; Woods, T.;
Mathioudakis, M.; Fletcher, L.; Kowalski, A.; Keenan, F.
Bibcode: 2012AAS...22052105M
Altcode:
Recent solar flare simulations suggest that the energy deposited in the
chromosphere by nonthermal electrons during a flare's impulsive phase
is re-emitted in the form of recombination (free-bound) continua, in
particular, the Lyman, Balmer, and Paschen continua of hydrogen, and
the He I and He II continua (Allred et al. 2005). However, definitive
observations of free-bound emission during solar flares have been scarce
in recent years as many modern, space-based instruments do not have
the required sensitivity, wavelength coverage, or duty cycle. With
the launch of SDO, these observations are now routinely available
thanks to the EUV Variability Experiment (EVE) instrument. Here we
present unambiguous, spectrally and temporally resolved detections of
enhanced free-free and free-bound continua during the first X-class
solar flare of Solar Cycle 24. While we find that the flare energy
in the EVE spectral range amounts to at most a few percent of the
total flare energy, these findings highlight the capability of EVE
in giving us the first comprehensive look at these diagnostically
important continuum components.
Title: Time-resolved NUV And Optical Spectra Of A Stellar Megaflare
On YZ CMi With SALT/RSS
Authors: Brown, Benjamin; Kowalski, A. F.; Mathioudakis, M.; Hooper,
E. J.; Hawley, S. L.; Osten, R. A.; Wisniewski, J. P.
Bibcode: 2012AAS...22020452B
Altcode:
The primary mode of radiative energy release in stellar flares is
in the optical and near-ultraviolet (NUV) continuum. Active M-dwarf
stares flare more frequently than the Sun, and their flares can be
substantially more energetic. The dominant component in solar flare
white light is thought to be Hydrogen recombination, whereas for stellar
M dwarf flares, the dominant component is thought to be T 10,000 K
blackbody emission. Recently we have obtained very high time-cadence
spectral observations of the flaring M-dwarf YZ CMi (3200-6000A) using
the Robert Stobie Spectrograph on the 11-meter South African Large
Telescope (SALT/RSS), achieving 100x better temporal resolution than
has previously been possible at the atmospheric limit. We observed
a megaflare of over 100x flux enhancement in the NUV emission. Here
we discuss the evolution of the stellar flare spectrum during the
rapid impulsive phase of the flare and the implications for stellar
flare models.
Title: Using Kepler Data to Characterize the Flare Properties of
GK Stars
Authors: Kowalski, Adam F.; Deitrick, Russell J.; Brown, Alex;
Davenport, Jim R. A.; Hawley, Suzanne L.; Hilton, Eric J.; Ayres,
Thomas R.; Berdyugina, Svetlana V.; Harper, Graham M.; Korhonen,
Heidi; Walkowicz, Lucianne M.
Bibcode: 2012decs.confE.120K
Altcode:
Due to their high occurrence rate and large contrast against the
background stellar emission, white-light flares on a handful of
very active low-mass M stars have been the primary source for our
understanding of optical flare emission. Kepler's high-precision, long
baseline light curves have opened up the characterization of white-light
emission to new domains of stars, including active G dwarfs. We present
the properties of white-light flares on GALEX-selected solar-type stars
from GO data in Q1-Q7. The flares are discussed in relation to intrinsic
stellar properties, which are constrained by a vast amount of follow-up
characterization of the sample. We compare the flare properties to
large white-light flares observed on the Sun. These high-precision
state-of-the-art observations will provide important constraints for
models of internal magnetic dynamos and NLTE radiative-hydrodynamic
simulations of energy deposition in the lower atmospheric layers.
Title: Observations of Enhanced Extreme Ultraviolet Continua during
an X-Class Solar Flare Using SDO/EVE
Authors: Milligan, Ryan O.; Chamberlin, Phillip C.; Hudson, Hugh S.;
Woods, Thomas N.; Mathioudakis, Mihalis; Fletcher, Lyndsay; Kowalski,
Adam F.; Keenan, Francis P.
Bibcode: 2012ApJ...748L..14M
Altcode: 2012arXiv1202.1731M
Observations of extreme ultraviolet (EUV) emission from an X-class solar
flare that occurred on 2011 February 15 at 01:44 UT are presented,
obtained using the EUV Variability Experiment (EVE) on board the
Solar Dynamics Observatory. The complete EVE spectral range covers
the free-bound continua of H I (Lyman continuum), He I, and He II,
with recombination edges at 91.2, 50.4, and 22.8 nm, respectively. By
fitting the wavelength ranges blueward of each recombination edge
with an exponential function, light curves of each of the integrated
continua were generated over the course of the flare, as was emission
from the free-free continuum (6.5-37 nm). The He II 30.4 nm and Lyα
121.6 nm lines, and soft X-ray (SXR; 0.1-0.8 nm) emission from GOES are
also included for comparison. Each free-bound continuum was found to
have a rapid rise phase at the flare onset similar to that seen in the
25-50 keV light curves from RHESSI, suggesting that they were formed
by recombination with free electrons in the chromosphere. However,
the free-free emission exhibited a slower rise phase seen also in the
SXR emission from GOES, implying a predominantly coronal origin. By
integrating over the entire flare the total energy emitted via
each process was determined. We find that the flare energy in the
EVE spectral range amounts to at most a few percent of the total
flare energy, but EVE gives us a first comprehensive look at these
diagnostically important continuum components.
Title: Multi-wavelength Characterization of Stellar Flares on Low-mass
Stars Using SDSS and 2MASS Time-domain Surveys
Authors: Davenport, James R. A.; Becker, Andrew C.; Kowalski, Adam
F.; Hawley, Suzanne L.; Schmidt, Sarah J.; Hilton, Eric J.; Sesar,
Branimir; Cutri, Roc
Bibcode: 2012ApJ...748...58D
Altcode: 2012arXiv1202.1902D
We present the first rates of flares from M dwarf stars in both red
optical and near-infrared (NIR) filters. We have studied ~50,000 M
dwarfs from the Sloan Digital Sky Survey (SDSS) Stripe 82 area and
1321 M dwarfs from the Two Micron All Sky Survey (2MASS) Calibration
Scan Point Source Working Database that overlap SDSS imaging fields. We
assign photometric spectral types from M0 to M6 using (r - i) and (i -
z) colors for every star in our sample. Stripe 82 stars each have 50-100
epochs of data, while 2MASS Calibration stars have ~1900 epochs. From
these data we estimate the observed rates and theoretical detection
thresholds for flares in eight photometric bands as a function of
spectral type. Optical flare rates are found to be in agreement with
previous studies, while the frequency per hour of NIR flare detections
is found to be more than two orders of magnitude lower. An excess
of small-amplitude flux increases in all bands exhibits a power-law
distribution, which we interpret as the result of flares below our
detection thresholds. In order to investigate the recovery efficiency
for flares in each filter, we extend a two-component flare model into
the NIR. Quiescent M0-M6 spectral templates were used with the model
to predict the photometric response of flares from u to Ks
. We determine that red optical filters are sensitive to flares with
u-band amplitudes gsim2 mag, and NIR filters to flares with Δu gsim
4.5 mag. Our model predicts that M0 stars have the best color contrast
for J-band detections, but M4-M6 stars should yield the highest rate of
NIR flares with amplitudes of ΔJ >= 0.01 mag. Characterizing flare
rates and photometric variations at longer wavelengths is important for
predicting the signatures of M dwarf variability in next-generation
surveys, and we discuss their impact on surveys such as the Large
Synoptic Survey Telescope.
Title: The Multiple Continuum Components in the White-Light Flare
of 16 January 2009 on the dM4.5e Star YZ CMi
Authors: Kowalski, A. F.; Hawley, S. L.; Holtzman, J. A.; Wisniewski,
J. P.; Hilton, E. J.
Bibcode: 2012SoPh..277...21K
Altcode: 2011arXiv1109.0837K
The white light during M dwarf flares has long been known to exhibit
the broadband shape of a T≈10 000 K blackbody, and the white
light in solar-flares is thought to arise primarily from hydrogen
recombination. Yet, a current lack of broad-wavelength coverage
solar flare spectra in the optical/near-UV region prohibits a direct
comparison of the continuum properties to determine if they are indeed
so different. New spectroscopic observations of a secondary flare
during the decay of a megaflare on the dM4.5e star YZ CMi have revealed
multiple components in the white-light continuum of stellar flares,
including both a blackbody-like spectrum and a hydrogen-recombination
spectrum. One of the most surprising findings is that these two
components are anti-correlated in their temporal evolution. We combine
initial phenomenological modeling of the continuum components with
spectra from radiative hydrodynamic models to show that continuum
veiling causes the measured anti-correlation. This modeling allows us
to use the components' inferred properties to predict how a similar
spatially resolved, multiple-component, white-light continuum might
appear using analogies to several solar-flare phenomena. We also
compare the properties of the optical stellar flare white light to
Ellerman bombs on the Sun.
Title: MMT Hectochelle Spectral Variability of Active Late-type
Stars in the Kepler Field (2012A)
Authors: Brown, Alexander; Walkowicz, Lucianne; Hawley, Suzanne;
Kowalski, Adam; Saar, Steven; Furesz, Gabor
Bibcode: 2012noao.prop..332B
Altcode:
We have on-going Kepler photometric monitoring of over 200 active
late-type (mid-A - K) stars as part of our Cycles 1/2/3 Guest Observer
(GO) programs with the aim of studying starspot evolution, differential
rotation, activity cycles, and flares. We propose to use the MMT
Hectochelle multiobject spectrograph to observe over 120 of these stars
to determine a range of basic physical properties for the stars, such
as radial velocity variations due to binarity, chromospheric activity
levels from Ca II H+K and H(alpha), projected rotational velocities
for comparison to the rotational periods measured directly by Kepler,
age/youth as indicated by Li I, and better effective temperature and
luminosity estimates. In addition, to provide a superior sample for
statistical studies another ~1,000 GKM dwarf stars showing either
starspot modulation from the Kepler Team's data or from our on-going
deep XMM X-ray survey will be observed using the unassigned fibers in
each field. These measurements require the 32,000 spectral resolution
provided by Hectochelle, which is hard to obtain efficiently for
13-15th magnitude stars any other way.
Title: Probing the Flare Atmospheres of M Dwarfs Using Infrared
Emission Lines
Authors: Schmidt, Sarah J.; Kowalski, Adam F.; Hawley, Suzanne L.;
Hilton, Eric J.; Wisniewski, John P.; Tofflemire, Benjamin M.
Bibcode: 2012ApJ...745...14S
Altcode: 2011arXiv1111.7072S
We present the results of a campaign to monitor active M dwarfs
using infrared spectroscopy, supplemented with optical photometry and
spectroscopy. We detected 16 flares during nearly 50 hr of observations
on EV Lac, AD Leo, YZ CMi, and VB 8. The three most energetic flares
also showed infrared emission, including the first reported detections
of Pβ, Pγ, He I λ10830, and Brγ during an M dwarf flare. The
strongest flare (Δu = 4.02 on EV Lac) showed emission from Hγ, Hδ,
He I λ4471, and Ca II K in the UV/blue and Pβ, Pγ, Pδ, Brγ,
and He I λ10830 in the infrared. The weaker flares (Δu = 1.68 on
EV Lac and ΔU = 1.38 on YZ CMi) were only observed with photometry
and infrared spectroscopy; both showed emission from Pβ, Pγ, and
He I λ10830. The strongest infrared emission line, Pβ, occurred in
the active mid-M dwarfs with a duty cycle of ~3%-4%. To examine the
most energetic flare, we used the static NLTE radiative transfer code
RH to produce model spectra based on a suite of one-dimensional model
atmospheres. Using a hotter chromosphere than previous one-dimensional
atmospheric models, we obtain line ratios that match most of the
observed emission lines. Based on observations obtained with the
Apache Point Observatory 3.5 m telescope, which is owned and operated
by the Astrophysical Research Consortium.
Title: The Implications of M Dwarf Flares on the Detection and
Characterization of Exoplanets at Infrared Wavelengths
Authors: Tofflemire, Benjamin M.; Wisniewski, John P.; Kowalski,
Adam F.; Schmidt, Sarah J.; Kundurthy, Praveen; Hilton, Eric J.;
Holtzman, Jon A.; Hawley, Suzanne L.
Bibcode: 2012AJ....143...12T
Altcode: 2011arXiv1111.1793T
We present the results of an observational campaign which obtained
high-cadence, high-precision, simultaneous optical and IR photometric
observations of three M dwarf flare stars for 47 hr. The campaign
was designed to characterize the behavior of energetic flare events,
which routinely occur on M dwarfs, at IR wavelengths to millimagnitude
precision, and quantify to what extent such events might influence
current and future efforts to detect and characterize extrasolar
planets surrounding these stars. We detected and characterized four
highly energetic optical flares having U-band total energies of
~7.8 × 1030 to ~1.3 × 1032 erg, and found no
corresponding response in the J, H, or Ks bandpasses at the precision of
our data. For active dM3e stars, we find that a ~1.3 × 1032
erg U-band flare (ΔU max ~ 1.5 mag) will induce <8.3
(J), <8.5 (H), and <11.7 (Ks) mmag of a response. A flare of
this energy or greater should occur less than once per 18 hr. For
active dM4.5e stars, we find that a ~5.1 × 1031 erg
U-band flare (ΔU max ~ 1.6 mag) will induce <7.8 (J),
<8.8 (H), and <5.1 (Ks) mmag of a response. A flare of this
energy or greater should occur less than once per 10 hr. No evidence
of stellar variability not associated with discrete flare events was
observed at the level of ~3.9 mmag over 1 hr timescales and at the
level of ~5.6 mmag over 7.5 hr timescales. We therefore demonstrate
that most M dwarf stellar activity and flares will not influence IR
detection and characterization studies of M dwarf exoplanets above
the level of ~5-11 mmag, depending on the filter and spectral type. We
speculate that the most energetic megaflares on M dwarfs, which occur
at rates of once per month, are likely to be easily detected in IR
observations with sensitivity of tens of millimagnitudes. We also
discuss how recent detections of line flux enhancements during M dwarf
flares could influence IR transmission spectroscopic observations of
M dwarf exoplanets.
Title: White-Light Continuum Emission in M Dwarf Flares
Authors: Kowalski, Adam; Hawley, S. L.
Bibcode: 2012AAS...21910403K
Altcode:
A primary mode of radiative energy release in stellar flares
is the optical and near-ultraviolet (NUV) continuum. However,
radiative-hydrodynamic models of stellar flares using a solar flare
paradigm and the sparse observations of solar and stellar flare continua
are all seemingly in disagreement over the type(s) of emission that
contribute to the optical/NUV continuum during flares. We have completed
a long-term flare monitoring campaign using simultaneous low-resolution
(3400-9200A) spectroscopic and broadband photometric observations to
fully characterize the optical/NUV white light continuum emission on
short timescales. To date, our most significant results come from
observations during the decay phase of a megaflare on the dM4.5e
star YZ CMi, where we have detected multiple continuum components
that contribute to the white light near the Balmer jump (3646A). We
present a time-resolved spectral analysis of the continuum components
and emission lines for this flare and for several other large and small
flares obtained during our spectroscopic monitoring campaign. We compare
these data to phenomenological flare models with the RH code and to
preliminary results from the next-generation of radiative-hydrodynamic
1D flare models with the RADYN code. Funding for this project
has been provided by NSF AST 0807205. Observations were obtained
with the ARC 3.5m, the NMSU 1m, and the ARCSAT 0.5m at the Apache
Point Observatory.
Title: Time-Resolved Properties and Global Trends in dMe Flares from
Simultaneous Photometry and Spectra
Authors: Kowalski, Adam F.
Bibcode: 2012PhDT.......179K
Altcode:
We present a homogeneous survey of near-ultraviolet (NUV) /optical line
and continuum emission during twenty M dwarf flares with simultaneous,
high cadence photometry and spectra. These data were obtained to
study the white-light continuum components to the blue and red of the
Balmer jump to break the degeneracy with fitting emission mechanisms to
broadband colors and to provide constraints for radiative-hydrodynamic
flare models that seek to reproduce the white-light flare emission. The
main results from the continuum analysis are the following: 1)
the detection of Balmer continuum (in emission) that is present
during all flares, with a wide range of relative contribution to the
continuum flux in the NUV; 2) a blue continuum at the peak of the
photometry that is linear with wavelength from λ = 4000 - 4800Å,
matched by the spectral shape of hot, blackbody emission with typical
temperatures of 10 000 - 12 000 K; 3) a redder continuum apparent at
wavelengths longer than Hβ; this continuum becomes relatively more
important to the energy budget during the late gradual phase. The hot
blackbody component and redder continuum component (which we call "the
conundruum") have been detected in previous UBVR colorimetry studies
of flares. With spectra, one can compare the properties and detailed
timings of all three components. Using time-resolved spectra during
the rise phase of three flares, we calculate the speed of an expanding
flare region assuming a simple geometry; the speeds are found to be ~5-
10 km s-1 and 50 - 120 km s -1, which are strikingly consistent with
the speeds at which two-ribbon flares develop on the Sun. The main
results from the emission line analysis are 1) the presentation of
the "time-decrement", a relation between the timescales of the Balmer
series; 2) a Neupert-like relation between Ca \pcy K and the blackbody
continuum, and 3) the detection of absorption wings in the Hydrogen
Balmer lines during times of peak continuum emission, indicative of
hot-star spectra forming during the flare. A byproduct of this study
is a new method for deriving absolute fluxes during M dwarf flare
observations obtained from narrow-slit spectra or during variable
weather conditions. This technique allows us to analyze the spectra
and photometry independently of one another, in order to connect the
spectral properties to the rise, peak, and decay phases of broadband
light curve morphology. We classify the light curve morphology according
to an "impulsiveness index" and find that the fast (impulsive) flares
have less Balmer continuum at peak emission than the slow (gradual)
flares. In the gradual phase, the energy budget of the flare spectrum
during almost all flares has a larger contribution from the Hydrogen
Balmer component than in the impulsive phase, suggesting that the
heating and cooling processes evolve over the course of a flare. We
find that, in general, the evolution of the hot blackbody is rapid,
and that the blackbody temperature decreases to ~8000 K in the gradual
phase. The Balmer continuum evolves more slowly than the blackbody ¨C
similar to the higher order Balmer lines but faster than the lower
order Balmer lines. The height of the Balmer jump increases during
the gradual decay phase. We model the Balmer continuum emission using
the RHD F11 model spectrum from Allred et al. (2006), but we discuss
several important systematic uncertainties in relating the apparent
amount of Balmer continuum to a given RHD beam model. Good fits to the
shape of the RHD F11 model spectrum are not obtained at peak times,
in contrast to the gradual phase. We model the blackbody component
using model hot star atmospheres from Castelli & Kurucz (2004)
in order to account for the effects of flux redistribution in the
flare atmosphere. This modeling is motivated by observations during
a secondary flare in the decay phase of a megaflare, when the newly
formed flare spectrum resembled that of Vega with the Balmer continuum
and lines in absorption. We model this continuum phenomenologically
with the RH code using hot spots placed at high column mass in the
M dwarf quiescent atmosphere; a superposition of hot spot models and
the RHD model are used to explain the anti-correlation in the apparent
amount of Balmer continuum in emission and the U-band light curve. We
attempt to reproduce the blackbody component in self-consistent 1D
radiative hydrodynamic flare models using the RADYN code. We simulate
the flare using a solar-type nonthermal electron beam heating function
with a total energy flux of 1012 ergs cm-2 s-1 (F12) for a duration of
5 seconds and a subsequent gradual phase. Although there is a larger
amount of NUV backwarming at log mc/(1g cm-2)~0 than in the F11 model,
the resulting flare continuum shape is similar to the F11 model spectrum
with a larger Balmer jump and a much redder spectral shape than is seen
in the observations. We do not find evidence of white-light emitting
chromospheric condensations, in contrast to the previous F12 model of
Livshits et al. (1981). We discuss future avenues for RHD modeling in
order to produce a hot blackbody component, including the treatment
of nonthermal protons in M dwarf flares.
Title: The Sloan Digital Sky Survey Data Release 7 M Dwarf
Spectroscopic Catalog
Authors: West, A. A.; Morgan, D. P.; Bochanski, J. J.; Andersen,
J. M.; Bell, K. J.; Kowalski, A. F.; Davenport, J. R. A.; Hawley,
S. L.; Schmidt, S. J.; Bernat, D.; Hilton, E. J.; Muirhead, P.;
Covey, K. R.; Rojas-Ayala, B.; Schlawin, E.; Gooding, M.; Schluns,
K.; Dhital, S.; Pineda, J. S.; Jones, D. O.
Bibcode: 2011ASPC..448.1407W
Altcode: 2010arXiv1012.3766W; 2011csss...16.1407W
We present a spectroscopic catalog of 70,841 visually inspected M
dwarfs from the seventh data release (DR7) of the Sloan Digital Sky
Survey (SDSS). For each spectrum, we provide measurements of the
spectral type, a number of molecular bandheads, and the Hα, Hβ,
Hγ, Hδ and Ca II K emission lines. In addition, we calculate the
metallicity-sensitive parameter ζ and 3D space motions for most of the
stars in the sample. Our catalog is cross-matched to Two Micron All Sky
Survey (2MASS) infrared data, and contains photometric distances for
each star. Future studies will use these data to thoroughly examine
magnetic activity and kinematics in late-type M dwarfs and examine
the chemical and dynamical history of the local Milky Way.
Title: Mining Databases for M Dwarf Variability
Authors: Davenport, J. R. A.; Becker, A. C.; Hawley, S. L.; Kowalski,
A. F.; Sesar, B.; Cutri, R. M.
Bibcode: 2011ASPC..448..983D
Altcode: 2011csss...16..983D; 2011arXiv1101.1363D
Time-resolved databases with large spatial coverage are quickly
becoming a standard tool for all types of astronomical studies. We
report preliminary results from our search for stellar flares in the
2MASS calibration fields. A sample of 4343 M dwarfs, spatially matched
between the SDSS and the 2MASS calibration fields, each with hundreds
to thousands of epochs in near infrared bandpasses, is analyzed using
a modified Welch-Stetson index to characterize the variability. A
Monte Carlo model was used to assess the noise of the variability
index. We find significnat residuals above the noise with power-law
slopes of -3.37 and -4.05 for our JH and HKs distributions
respectively. This is evidence for flares being observed from M dwarfs
in infrared photometry.
Title: M Dwarf Flares: Exoplanet Detection Implications
Authors: Tofflemire, B. M.; Wisniewski, J. P.; Hilton, E. J.; Kowalski,
A. F.; Kundurthy, P.; Schmidt, S. J.; Hawley, S. L.; Holtzman, J. A.
Bibcode: 2011ASPC..448.1287T
Altcode: 2011csss...16.1287T
Low mass stars such as M dwarfs have become prime targets for exoplanet
transit searches as their low luminosities and small stellar radii
could enable the detection of super-Earths residing in their habitable
zones. While promising transit targets, M dwarfs are also inherently
variable and can exhibit up to ∼6 magnitude flux enhancements in
the optical U-band. This is significantly higher than the predicted
transit depths of habitable zone super-Earths (0.005 magnitude
flux decrease). The behavior of flares at infrared (IR) wavelengths,
particularly those likely to be used to study and characterize M dwarf
exoplanets using facilities such as the James Web Space Telescope
(JWST), remains largely unknown. To address these uncertainties, we
are executing a coordinated, contemporaneous monitoring program of
the optical and IR flux of M dwarfs known to regularly flare. A suite
of telescopes located at the Kitt Peak National Observatory and the
Apache Point Observatory are used for the observations. We present
the initial results of this program.
Title: White Light Flare Continuum Observations with ULTRACAM
Authors: Kowalski, A. F.; Mathioudakis, M.; Hawley, S. L.; Hilton,
E. J.; Dhillon, V. S.; Marsh, T. R.; Copperwheat, C. M.
Bibcode: 2011ASPC..448.1157K
Altcode: 2011arXiv1103.0822K; 2011csss...16.1157K
We present sub-second, continuous-coverage photometry of three flares
on the dM3.5e star, EQ Peg A, using custom continuum filters with
WHT/ULTRACAM. These data provide a new view of flare continuum emission,
with each flare exhibiting a very distinct light curve morphology. The
spectral shape of flare emission for the two large-amplitude flares
is compared with synthetic ULTRACAM measurements taken from the
spectra during the large 'megaflare' event on a similar type flare
star. The white light shape during the impulsive phase of the EQ
Peg flares is consistent with the range of colors derived from the
megaflare continuum, which is known to contain a Hydrogen recombination
component and compact, blackbody-like components. Tentative evidence
in the ULTRACAM photometry is found for an anti-correlation between
the emission of these components.
Title: The Galactic M Dwarf Flare Rate
Authors: Hilton, E. J.; Hawley, S. L.; Kowalski, A. F.; Holtzman, J.
Bibcode: 2011ASPC..448..197H
Altcode: 2011csss...16..197H
M dwarfs are known to flare on timescales from minutes to hours,
with flux increases of several magnitudes in the blue/near-UV. These
frequent, powerful events, which are caused by magnetic reconnection,
will have a strong observational signature in large, time-domain
surveys. The radiation and particle fluxes from flares may also exert
a significant influence on the atmospheres of orbiting planets, and
affect their habitability. We present a statistical model of flaring
M dwarfs in the Galaxy that allows us to predict the observed flare
rate along a given line of sight for a particular survey depth and
cadence. The parameters that enter the model are the Galactic structure,
the distribution of magnetically active and inactive M dwarfs, and
the flare frequency distribution (FFD) of both populations. The FFD is
a function of spectral type, activity, and Galactic height. Although
inactive M dwarfs make up the majority of stars in a magnitude-limited
survey, the FFD of inactive stars is very poorly constrained. We
have organized a flare monitoring campaign comprising hundreds of
hours of new observations from both the ground and space to better
constrain flare rates. Incorporating the new observations into our
model provides more accurate predictions of stellar variability caused
by flares on M dwarfs. We pay particular attention to the likelihood
of flares appearing as optical transients (i.e., host star not seen
in quiescent data).
Title: Splinter Session "Solar and Stellar Flares"
Authors: Fletcher, L.; Hudson, H.; Cauzzi, G.; Getman, K. V.; Giampapa,
M.; Hawley, S. L.; Heinzel, P.; Johnstone, C.; Kowalski, A. F.; Osten,
R. A.; Pye, J.
Bibcode: 2011ASPC..448..441F
Altcode: 2011csss...16..441F; 2012arXiv1206.3997F
This summary reports on papers presented at the Cool Stars-16 meeting in
the splinter session "Solar and Stellar flares." Although many topics
were discussed, the main themes were the commonality of interests,
and of physics, between the solar and stellar flare communities,
and the opportunities for important new observations in the near future.
Title: An ``A star'' on an M star during a flare within a flare
Authors: Kowalski, Adam F.; Hawley, Suzanne L.; Holtzman, Jon A.;
Wisniewski, John P.; Hilton, Eric J.
Bibcode: 2011IAUS..273..261K
Altcode: 2010arXiv1010.0452K
M dwarfs produce explosive flare emission in the near-UV and optical
continuum, and the mechanism responsible for this phenomenon is not
well-understood. We present a near-UV/optical flare spectrum from the
rise phase of a secondary flare, which occurred during the decay of
a much larger flare. The newly formed flare emission resembles the
spectrum of an early-type star, with the Balmer lines and continuum
in absorption. We model this observation phenomenologically as a
temperature bump (hot spot) near the photosphere of the M dwarf. The
amount of heating implied by our model (ΔTphot ~ 16,000 K)
is far more than predicted by chromospheric backwarming in current 1D
RHD flare models (ΔTphot ~ 1200 K).
Title: Starspot variability and evolution from modeling Kepler
photometry of active late-type stars
Authors: Brown, Alexander; Korhonen, Heidi; Berdyugina, Svetlana;
Tofany, Barton; Ayres, Thomas R.; Kowalski, Adam; Hawley, Suzanne;
Harper, Graham; Piskunov, Nikolai
Bibcode: 2011IAUS..273...78B
Altcode:
The Kepler satellite provides a unique opportunity to study the detailed
optical photometric variability of late-type stars with unprecedentedly
long (several year) continuous monitoring and sensitivity to very
small-scale variations. We are studying a sample of over two hundred
cool (mid-A - late-K spectral type) stars using Kepler long-cadence
(30 minute sampling) observations. These stars show a remarkable
range of photometric variability, but in this paper we concentrate on
rotational modulation due to starspots and flaring. Modulation at the
0.1% level is readily discernable. We highlight the rapid timescales
of starspot evolution seen on solar-like stars with rotational periods
between 2 and 7 days.
Title: The First Detection of Time-Variable Infrared Line Emission
During M Dwarf Flares
Authors: Schmidt, Sarah J.; Hilton, E. J.; Tofflemire, B.; Wisniewski,
J. P.; Kowalski, A. F.; Holtzman, J.; Hawley, S. L.
Bibcode: 2011AAS...21832604S
Altcode: 2011BAAS..43G32604S
M dwarfs are notorious for their active chromospheres, characterized by
quiescent line emission at optical wavelengths in addition to dramatic
flare events. These flares have been well-studied at X-ray, radio,
UV, and optical wavelengths, but so far there is only one single-epoch
detection of high-order Paschen emission lines in a red optical spectrum
(Schmidt et al. 2007). In order to investigate infrared line emission
during flares, we have conducted a monitoring campaign totaling
about 60 hours on 5 active M dwarfs. We have obtained infrared (0.9
to 2.4 micron) spectroscopy using the TripleSpec instrument on the
Apache Point Observatory 3.5-m, simultaneous optical/UV photometry
on the NMSU 1-m and ARC 0.8-m, and optical spectroscopy on the DAO
1.8-m for one run. During the three brightest flares observed on EV
Lac and YZ CMi (> 2 magnitudes in U), we observed emission from
Hydrogen Paschen beta, gamma, and delta; Brackett gamma, and Helium
10830A. We characterize the strength and time variation of these
lines and investigate the heating needed to produce infrared emission
during flares.
Title: Light Curves, Energetics and Rates of M Dwarf Flares
Authors: Hilton, Eric J.; Hawley, S. L.; Kowalski, A. F.; Schmidt,
S. J.; Davenport, J. R. A.; Wisniewski, J. P.; Bell, K. J.; Tofflemire,
B.; Holtzman, J.
Bibcode: 2011AAS...21832502H
Altcode: 2011BAAS..43G32502H
The magnetic reconnection events that power stellar flares lead to a
wide variety of light curve shapes, hinting at the complex underlying
magnetic field topologies. Using our quantitative definition of a flare
event, we find more than 100 flares during 600 hours of photometric
monitoring of two dozen stars. The sample includes both active and
inactive M dwarfs with a range of spectral type. We fit models for the
light curve evolution to our photometric flare catalogue and present
an analysis of the rise and decay times as well as flare colors. We
additionally present the distribution of flare rates as a function of
energy and equivalent duration. The flare frequency distribution is
used to characterize the impact of M dwarf flares seen in time domain
surveys, and is also necessary to model the effect of flares on the
atmospheres of exoplanets orbiting an M dwarf host.
Title: High Cadence Kepler Observations of Flare Stars
Authors: Hawley, Suzanne L.; Kowalski, A. F.; Wisniewski, J. P.;
Hilton, E. J.; Walkowicz, L. M.; Brown, A.
Bibcode: 2011AAS...21822705H
Altcode: 2011BAAS..43G22705H
We report on preliminary results from our Kepler Cycle 2 GO program to
observe low mass stars at high cadence (one observation per minute). The
outstanding fidelity of the Kepler light curves reveals both starspot
modulation and a large number of stellar flares. We investigate the
flare amplitude, frequency and energy distributions and relate these
to the better-known nearby flare stars in the solar neighborhood.
Title: UV Diagnostics of Stellar and Solar Flares
Authors: Kowalski, Adam; Hawley, S. L.; Hudson, H. S.
Bibcode: 2011AAS...21821303K
Altcode: 2011BAAS..43G21303K
The UV spectral regime provides a comprehensive view of the plasma
dynamics and atmospheric temperature structure during stellar flares. We
review the major developments in UV spectroscopy of flares on low mass
stars that shape our understanding of the flare process and challenge
the predictions of current radiative hydrodynamic models. We put the
ultraviolet properties in context with the radiation in the neighboring
X-ray and visible wavelength regimes. We also show how SDO/EVE data
of several Cycle 24 solar flares allow for new comparisons to be made
between solar and stellar flares.
Title: M Dwarf Photometric Variability In The Optical And NIR
Authors: Davenport, James R. A.; Becker, A. C.; Kowalski, A. F.;
Hawley, S. L.; Hilton, E. J.
Bibcode: 2011AAS...21832603D
Altcode: 2011BAAS..43G32603D
We present limits on the observability of stochastic flare events from
M dwarfs in SDSS and 2MASS filters. We have studied 30,000 M dwarfs
from the SDSS Stripe 82 time-domain catalog, and 4300 M dwarfs from the
2MASS Calibration Scan Point Source Working Database which overlap the
SDSS DR7 single-epoch data. M dwarfs are chosen based on their SDSS
r,i,z colors. Stripe 82 stars each have 50-100 epochs of data, while
2MASS Calibration stars have 2000-3000. An M dwarf continuum spectral
model is used to predict observed flare signatures in each band. From
these data we estimate the observed rates and theoretical detection
thresholds for flares in eight photometric bands as a function of
spectral type. The structure function of the variability for each
spectral type bin is also calculated for all eight bands. These
rates of flares and photometric variations at longer wavelengths
will be important for predicting the impact of M dwarf variability in
next-generation instruments such as JWST.
Title: Kepler Observations of Starspot Evolution, Differential
Rotation, and Flares on Late-Type Stars
Authors: Brown, Alexander; Korhonen, H.; Berdyugina, S.; Walkowicz,
L.; Kowalski, A.; Hawley, S.; Neff, J.; Ramsey, L.; Redman, S.; Saar,
S.; Furesz, G.; Piskunov, N.; Harper, G.; Ayres, T.; Tofany, B.
Bibcode: 2011AAS...21820502B
Altcode: 2011BAAS..43G20502B
The Kepler satellite is providing spectacular optical photometric
light-curves of unprecedented precision and duration that
routinely allow detailed studies of stellar magnetic activity on
late-type stars that were difficult, if not impossible, to attempt
previously. Rotational modulation due to starspots is commonly seen
in the Kepler light-curves of late-type stars, allowing detailed
study of the surface distribution of their photospheric magnetic
activity. Kepler is providing multi-year duration light-curves that
allow us to investigate how activity phenomena -- such as the growth,
migration, and decay of starspots, differential rotation, activity
cycles, and flaring -- operate on single and binary stars with a
wide range of mass and convection zone depth. We present the
first results from detailed starspot modeling using newly-developed
light-curve inversion codes for a range of GALEX-selected stars with
typical rotation periods of a few days, that we have observed as part of
our 200 target Kepler Cycle 1/2 Guest Observer programs. The physical
properties of the stars have been measured using high resolution
optical spectroscopy, which allows the Kepler results to be placed
within the existing framework of knowledge regarding stellar magnetic
activity. These results demonstrate the powerful diagnostic capability
provided by tracking starspot evolution essentially continuously for
more than 16 months. The starspots are clearly sampling the stellar
rotation rate at different latitudes, enabling us to measure the
differential rotation and starspot lifetimes. As would be expected,
stars with few day rotation show frequent flaring that is easily seen
as "white-light" flares in Kepler light-curves. We compare the observed
flare rates and occurrence with the starspot properties. This work
contains results obtained using the NASA Kepler satellite and from the
Apache Point Observatory, the MMT (using NOAO community access time),
and the Hobby-Eberly Telescope. Funding is provided by NASA Kepler
grants NNX10AC51G and NNX11AC79G.
Title: Kepler Observations of Pulsations In A Sample of
Magnetically-Active Stars
Authors: Neff, James E.; Brown, A.; Hawley, S.; Kowalski, A.;
Walkowicz, L.; Saar, S.
Bibcode: 2011AAS...21822704N
Altcode: 2011BAAS..43G22704N
We have observed about 200 targets in Kepler Cycle 1/2 Guest Observer
programs. The sample of active star candidates was selected primarily
using GALEX colors, and the Kepler light curves have revealed a rich
variety of variability. Rotational modulation (typical periods a few
days) due to starspots over the multi-year timeline of the Kepler
observations will permit us to measure surface differential rotation
and stellar magnetic cycles. On shorter timescales, the Kepler data
show dramatic evidence of stellar pulsations across much of the HR
diagram. Our selection criteria yielded a sample of magnetically active
G and K dwarfs, which might show solar-like pulsations. It also yielded
subsamples of several well-known pulsators (e.g., Delta Scuti stars)
as well as pulsators that currently defy easy classification. We are
systematically classifying and analyzing the pulsating stars in the our
Kepler GO program. We are particularly interested in using pulsations
to probe the interior properties of active G and K dwarfs, while the
starspots serve as a probe of the convection zone and surface layers. We
will present summary results for several different types of pulsation,
and we will provide a detailed asteroseismic analysis of those stars
in our sample that were observed to have both pulsations and magnetic
activity. This work contains results obtained using the NASA
Kepler satellite and from the Apache Point Observatory, the MMT (using
NOAO community access time), and the Hobby-Eberly Telescope. Funding
is provided by NASA Kepler grants NNX10AC51G and NNX11AC79G.
Title: Subterranean CO2 ventilation and its role in the
net ecosystem carbon balance of a karstic shrubland
Authors: Sanchez-Cañete, E. P.; Serrano-Ortiz, P.; Kowalski, A. S.;
Oyonarte, C.; Domingo, F.
Bibcode: 2011GeoRL..38.9802S
Altcode: 2011GeoRL..3809802S
Recent studies of carbonate ecosystems suggest a possible
contribution of subterranean ventilation to the net ecosystem carbon
balance. However, both the overall importance of such CO2
exchange processes and their drivers remain unknown. Here we
analyze several dry-season episodes of net CO2 emissions
to the atmosphere, along with soil and borehole CO2
measurements. Results highlight important events where rapid decreases
of underground CO2 molar fractions correlate well with
sizeable CO2 release to the atmosphere. Such events, with
high friction velocities, are attributed to ventilation processes, and
should be accounted for by predictive models of surface CO2
exchange.
Title: Periodic Variability of Low-mass Stars in Sloan Digital Sky
Survey Stripe 82
Authors: Becker, A. C.; Bochanski, J. J.; Hawley, S. L.; Ivezić,
Ž.; Kowalski, A. F.; Sesar, B.; West, A. A.
Bibcode: 2011ApJ...731...17B
Altcode: 2011arXiv1102.1387B
We present a catalog of periodic stellar variability in the "Stripe
82" region of the Sloan Digital Sky Survey. After aggregating
and re-calibrating catalog-level data from the survey, we ran a
period-finding algorithm (Supersmoother) on all point-source light
curves. We used color selection to identify systems that are likely to
contain low-mass stars, in particular M dwarfs and white dwarfs. In
total, we found 207 candidates, the vast majority of which appear to
be in eclipsing binary systems. The catalog described in this paper
includes 42 candidate M dwarf/white dwarf pairs, four white dwarf
pairs, 59 systems whose colors indicate they are composed of two
M dwarfs and whose light-curve shapes suggest they are in detached
eclipsing binaries, and 28 M dwarf systems whose light-curve shapes
suggest they are in contact binaries. We find no detached systems
with periods longer than 3 days, thus the majority of our sources
are likely to have experienced orbital spin-up and enhanced magnetic
activity. Indeed, 26 of 27 M dwarf systems that we have spectra for
show signs of chromospheric magnetic activity, far higher than the 24%
seen in field stars of the same spectral type. We also find binaries
composed of stars that bracket the expected boundary between partially
and fully convective interiors, which will allow the measurement of the
stellar mass-radius relationship across this transition. The majority
of our contact systems have short orbital periods, with small variance
(0.02 days) in the sample near the observed cutoff of 0.22 days. The
accumulation of these stars at short orbital period suggests that the
process of angular momentum loss, leading to period evolution, becomes
less efficient at short periods. These short-period systems are in a
novel regime for studying the effects of orbital spin-up and enhanced
magnetic activity, which are thought to be the source of discrepancies
between mass-radius predictions and measurements of these properties
in eclipsing binaries.
Title: The Sloan Digital Sky Survey Data Release 7 Spectroscopic M
Dwarf Catalog. I. Data
Authors: West, Andrew A.; Morgan, Dylan P.; Bochanski, John J.;
Andersen, Jan Marie; Bell, Keaton J.; Kowalski, Adam F.; Davenport,
James R. A.; Hawley, Suzanne L.; Schmidt, Sarah J.; Bernat, David;
Hilton, Eric J.; Muirhead, Philip; Covey, Kevin R.; Rojas-Ayala,
Bárbara; Schlawin, Everett; Gooding, Mary; Schluns, Kyle; Dhital,
Saurav; Pineda, J. Sebastian; Jones, David O.
Bibcode: 2011AJ....141...97W
Altcode: 2011arXiv1101.1082W
We present a spectroscopic catalog of 70,841 visually inspected M dwarfs
from the seventh data release of the Sloan Digital Sky Survey. For each
spectrum, we provide measurements of the spectral type, a number of
molecular band heads, and the Hα, Hβ, Hγ, Hδ, and Ca II K emission
lines. In addition, we calculate the metallicity-sensitive parameter ζ
and identify a relationship between ζ and the g - r and r - z colors
of M dwarfs. We assess the precision of our spectral types (which were
assigned by individual examination), review the bulk attributes of
the sample, and examine the magnetic activity properties of M dwarfs,
in particular those traced by the higher order Balmer transitions. Our
catalog is cross-matched to Two Micron All Sky Survey infrared data,
and contains photometric distances for each star. Finally, we identify
eight new late-type M dwarfs that are possibly within 25 pc of the
Sun. Future studies will use these data to thoroughly examine magnetic
activity and kinematics in late-type M dwarfs and examine the chemical
and dynamical history of the local Milky Way.
Title: M Dwarf Flares: Exoplanet Implications
Authors: Wisniewski, John; Kowalski, Adam; Schmidt, Sarah; Kundurthy,
Praveen; Hawley, Suzanne; Tofflemire, Ben; Holtzman, Jon
Bibcode: 2011noao.prop..106W
Altcode:
M dwarfs are attractive stars for exoplanet transit research as their
low luminosities and small stellar radii could enable detection of
super-Earths residing in their habitable zones. M dwarf flare events
can cause <0.1 to 6.0 magnitude flux enhancements in the optical U-
band, which is significantly higher than the predicted transit depths
of super-Earths (~0.005 magnitude flux decrease). While Solar flares
have been observed to cause infrared continuum enhancements (Xu et al
2006); surprisingly, it is not known whether energetic flares associated
with M dwarfs can induce IR variability in filters relevant to future
transiting exoplanet characterization studies (e.g. using JWST). We
propose to monitor the optical & IR flux of a M dwarf known to
regularly flare, to determine what effect flares could have on future IR
characterization studies of M dwarf exoplanets. This proposal represents
a resubmission of our approved 2009B program, which lost >80% of
its on-sky time due to Tropical Storm Olaf (but did demonstrate the
ability to achieve 5 milli-mag IR photometry with the KPNO 2.1m). We
request 5 nights in 2011A to complete our science goals.
Title: Extending M Dwarf Variability Studies to Longer Wavelengths
Authors: Davenport, James R. A.; Becker, A.; Kowalski, A. F.; Hilton,
E. J.; Hawley, S. L.
Bibcode: 2011AAS...21724213D
Altcode: 2011BAAS...4324213D
Flares on M dwarfs occur stochastically, and the statistical frequency
of such events is well characterized in the optical. Flares and stellar
variability are a source of confusion for large time-domain surveys,
and a unified physical model of these magnetically driven events across
all spectral types still awaits discovery. To correctly predict the
occurrence rate of M dwarf variability in future astronomical surveys,
we must understand the full SED of these events as completely as
possible. We have constructed a sample of 4000 M dwarfs with a broad
range of properties, each with thousands of epochs of observation. This
matched data set comes from the SDSS Stripe 82 and LINEAR databases
in the optical, and 2MASS Calibration Scan database in the NIR. We
present preliminary results that extend the flaring rate and variability
signature to longer wavelengths, where many future scientific missions
such as LSST, JWST, and others will operate.
Title: Revealing Stellar Magnetic Fields Through M Dwarf Flares
Authors: Hilton, Eric J.; Hawley, S. L.; Kowalski, A. F.
Bibcode: 2011AAS...21730702H
Altcode: 2011BAAS...4330702H
Magnetic reconnection on M dwarfs powers explosive flares with flux
increases of several magnitudes in the blue/near-UV on timescales
of minutes to hours. We obtained over 500 hours of flare monitoring
observations at the Apache Point Observatory to make the first
measurements of the flare frequency distribution of inactive early
and mid M dwarfs and active late M dwarfs. These new measurements
combined with our studies of flare rates from both SDSS photometry and
spectroscopy have allowed us to construct a model of M dwarf flaring in
the Galaxy that predicts the number and magnitude of flares expected
in a given survey. In addition to the implications for time-domain
surveys such as LSST, Pan-STARRS, and PTF, and for planet-habitability,
the rate of flaring on stars of different mass and age informs our
knowledge of the formation and evolution of stellar magnetic fields. We
find that the flare star distribution is more concentrated toward the
Galactic mid-plane than the active star population, implying that they
are younger. Active stars flare more frequently and with more energy
than inactive stars. Flares on late-type active M dwarfs are less
energetic than those on earlier types. We acknowledge support
from NSF grant AST 08-07205.
Title: An Optical Flare Rate Census of Galactic Bulge Dwarf Stars
Authors: Kowalski, Adam; Osten, R. A.; Sahu, K. C.; Hawley, S. L.
Bibcode: 2011AAS...21734207K
Altcode: 2011BAAS...4334207K
Flare emission is thought to be the observational consequence of
transiently heated plasma by the dynamic interaction of magnetic fields
throughout the stellar atmosphere. Other magnetic activity measures
indicate that age may be a fundamental parameter for the generation and
presence of surface magnetic fields. However, flares have been observed
on both old and young stars, and the importance of age on the flare
rate of a stellar population is not well known, as previous flare rate
studies have been limited to the surrounding solar neighborhood and
young disk population. The SWEEPS project monitored a 202x202 arcsec
dense stellar field in the Sagittarius window of the Galactic bulge for
a continuous seven-day period using the HST/ACS F606W (V) and F814W (I)
filters. These data were aimed at a search for transiting exoplanets,
but the high-cadence light curves, consisting of 260 epochs in each
filter, provide a unique repository to mine for flare incidence in an
evolved stellar population of dwarfs. We employ a customized algorithm
to search for flares on 200,000 cool dwarfs of intermediate-old age,
and we study the stellar flare rate and flare properties as a function
of mass, V - I color, and the degree of underlying variability. These
rates allow us to compare to the flare rates of younger stars and to
extend the investigation of the evolution of magnetic activity to an
older stellar population.
Title: Making The Most Of Flaring M Dwarfs
Authors: Hunt-Walker, Nicholas; Hilton, E.; Kowalski, A.; Hawley,
S.; Matthews, J.; Holtzman, J.
Bibcode: 2011AAS...21724224H
Altcode: 2011BAAS...4324224H
We present observations of flare activity using the Microvariability
and Oscillations of Stars (MOST) satellite in conjunction with
simultaneous spectroscopic and photometric observations from the ARC
3.5-meter, NMSU 1.0-meter, and ARCSAT 0.5-meter telescopes at the
Apache Point Observatory. The MOST observations enable unprecedented
completeness with regard to observing frequent, low-energy flares on
the well-known dMe flare star AD Leo with broadband photometry. The
observations span approximately one week with a 60-second cadence and
are sensitive to flares as small as 0.01-magnitudes. The time-resolved,
ground-based spectroscopy gives measurements of Hα and other important
chromospheric emission lines, whereas the Johnson U-, SDSS u-, and SDSS
g-band photometry provide color information during the flare events
and allow us to relate the MOST observations to decades of previous
broadband observations. Understanding the rates and energetics of flare
events on M dwarfs will help characterize this source of variability in
large time-domain surveys such as LSST and Pan-STARRS. Flare rates are
also of interest to astrobiology, since flares affect the habitability
of exoplanets orbiting M dwarfs.
Title: M Dwarf Flares from Time-resolved Sloan Digital Sky Survey
Spectra
Authors: Hilton, Eric J.; West, Andrew A.; Hawley, Suzanne L.;
Kowalski, Adam F.
Bibcode: 2010AJ....140.1402H
Altcode: 2010arXiv1009.1158H
We have identified 63 flares on M dwarfs from the individual component
spectra in the Sloan Digital Sky Survey (SDSS) using a novel measurement
of emission-line strength called the Flare Line Index. Each of the
~38,000 M dwarfs in the SDSS low-mass star spectroscopic sample of West
et al. was observed several times (usually 3-5) in exposures that were
typically 9-25 minutes in duration. Our criteria allowed us to identify
flares that exhibit very strong Hα and Hβ emission-line strength
and/or significant variability in those lines throughout the course of
the exposures. The flares we identified have characteristics consistent
with flares observed by classical spectroscopic monitoring. The flare
duty cycle for the objects in our sample is found to increase from 0.02%
for early M dwarfs to 3% for late M dwarfs. We find that the flare duty
cycle is larger in the population near the Galactic plane and that
the flare stars are more spatially restricted than the magnetically
active but non-flaring stars. This suggests that flare frequency may
be related to stellar age (younger stars are more likely to flare)
and that the flare stars are younger than the mean active population.
Title: Solar Flares and the Chromosphere
Authors: Fletcher, L.; Turkmani, R.; Hudson, H. S.; Hawley, S. L.;
Kowalski, A.; Berlicki, A.; Heinzel, P.
Bibcode: 2010arXiv1011.4650F
Altcode:
A white paper prepared for the Space Studies Board, National Academy
of Sciences (USA), for its Decadal Survey of Solar and Space Physics
(Heliophysics), reviewing and encouraging studies of flare physics in
the chromosphere.
Title: Solar Flares and the Chromosphere: A white paper for the
Decadal Survey
Authors: Hudson, H. S.; Fletcher, L.; Turkmani, R.; Hawley, S. L.;
Kowalski, A. F.; Berlicki, A.; Heinzel, P.
Bibcode: 2010helio2010....1H
Altcode:
No abstract at ADS
Title: The Milky Way Tomography with SDSS. III. Stellar Kinematics
Authors: Bond, Nicholas A.; Ivezić, Željko; Sesar, Branimir; Jurić,
Mario; Munn, Jeffrey A.; Kowalski, Adam; Loebman, Sarah; Roškar,
Rok; Beers, Timothy C.; Dalcanton, Julianne; Rockosi, Constance M.;
Yanny, Brian; Newberg, Heidi J.; Allende Prieto, Carlos; Wilhelm, Ron;
Lee, Young Sun; Sivarani, Thirupathi; Majewski, Steven R.; Norris,
John E.; Bailer-Jones, Coryn A. L.; Re Fiorentin, Paola; Schlegel,
David; Uomoto, Alan; Lupton, Robert H.; Knapp, Gillian R.; Gunn,
James E.; Covey, Kevin R.; Allyn Smith, J.; Miknaitis, Gajus; Doi,
Mamoru; Tanaka, Masayuki; Fukugita, Masataka; Kent, Steve; Finkbeiner,
Douglas; Quinn, Tom R.; Hawley, Suzanne; Anderson, Scott; Kiuchi,
Furea; Chen, Alex; Bushong, James; Sohi, Harkirat; Haggard, Daryl;
Kimball, Amy; McGurk, Rosalie; Barentine, John; Brewington, Howard;
Harvanek, Mike; Kleinman, Scott; Krzesinski, Jurek; Long, Dan; Nitta,
Atsuko; Snedden, Stephanie; Lee, Brian; Pier, Jeffrey R.; Harris,
Hugh; Brinkmann, Jonathan; Schneider, Donald P.
Bibcode: 2010ApJ...716....1B
Altcode: 2009arXiv0909.0013B
We study Milky Way kinematics using a sample of 18.8 million
main-sequence stars with r < 20 and proper-motion measurements
derived from Sloan Digital Sky Survey (SDSS) and POSS astrometry,
including ~170,000 stars with radial-velocity measurements from the
SDSS spectroscopic survey. Distances to stars are determined using a
photometric-parallax relation, covering a distance range from ~100
pc to 10 kpc over a quarter of the sky at high Galactic latitudes
(|b|>20°). We find that in the region defined by 1 kpc <Z<
5 kpc and 3 kpc <R< 13 kpc, the rotational velocity for disk
stars smoothly decreases, and all three components of the velocity
dispersion increase, with distance from the Galactic plane. In contrast,
the velocity ellipsoid for halo stars is aligned with a spherical
coordinate system and appears to be spatially invariant within the
probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M
stars is complex, and cannot be described by a standard Schwarzschild
ellipsoid. For stars in a distance-limited subsample of stars (<100
pc), we detect a multi-modal velocity distribution consistent with
that seen by HIPPARCOS. This strong non-Gaussianity significantly
affects the measurements of the velocity-ellipsoid tilt and vertex
deviation when using the Schwarzschild approximation. We develop and
test a simple descriptive model for the overall kinematic behavior
that captures these features over most of the probed volume, and can be
used to search for substructure in kinematic and metallicity space. We
use this model to predict further improvements in kinematic mapping of
the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.
Title: A White Light Megaflare on the dM4.5e Star YZ CMi
Authors: Kowalski, Adam F.; Hawley, Suzanne L.; Holtzman, Jon A.;
Wisniewski, John P.; Hilton, Eric J.
Bibcode: 2010ApJ...714L..98K
Altcode: 2010arXiv1003.3057K
On UT 2009 January 16, we observed a white light megaflare on the dM4.5e
star YZ CMi as part of a long-term spectroscopic flare-monitoring
campaign to constrain the spectral shape of optical flare continuum
emission. Simultaneous U-band photometric and 3350-9260 Å spectroscopic
observations were obtained during 1.3 hr of the flare decay. The event
persisted for more than 7 hr and at flare peak, the U-band flux was
almost 6 mag brighter than in the quiescent state. The properties of
this flare mark it as one of the most energetic and longest-lasting
white light flares ever to be observed on an isolated low-mass star. We
present the U-band flare energetics and a flare continuum analysis. For
the first time, we show convincingly with spectra that the shape
of the blue continuum from 3350 Å to 4800 Å can be represented
as a sum of two components: a Balmer continuum as predicted by the
Allred et al. radiative hydrodynamic flare models and a T~ 10,000 K
blackbody emission component as suggested by many previous studies of
the broadband colors and spectral distributions of flares. The areal
coverage of the Balmer continuum and blackbody emission regions vary
during the flare decay, with the Balmer continuum emitting region
always being significantly (~3-16 times) larger. These data will
provide critical constraints for understanding the physics underlying
the mysterious blue continuum radiation in stellar flares. Based on
observations obtained with the Apache Point Observatory 3.5 m Telescope,
which is owned and operated by the Astrophysical Research Consortium.
Title: Disk-Loss and Disk-Renewal Phases in Classical Be
Stars. I. Analysis of Long-Term Spectropolarimetric Data
Authors: Wisniewski, John P.; Draper, Zachary H.; Bjorkman, Karen S.;
Meade, Marilyn R.; Bjorkman, Jon E.; Kowalski, Adam F.
Bibcode: 2010ApJ...709.1306W
Altcode: 2009arXiv0912.1504W
Classical Be stars are known to occasionally transition from having
a gaseous circumstellar disk ("Be phase") to a state in which all
observational evidence for the presence of these disks disappears
("normal B-star phase"). We present one of the most comprehensive
spectropolarimetric views to date of such a transition for two Be
stars, π Aquarii and 60 Cygni.The disk-loss episode of 60 Cyg was
characterized by a generally monotonic decrease in emission strength
over a timescale of ~1000 days from the maximum V-band polarization
to the minimum Hα equivalent width, consistent with the viscous
timescale of the disk, assuming α~0.14. π Aqr's disk loss was
episodic in nature and occurred over a timescale of ~2440 days. An
observed time lag between the behavior of the polarization and Hα in
both stars indicates the disk clearing proceeded in an "inside-out"
manner. We determine the position angle of the intrinsic polarization
to be 166fdg7 ± 0fdg1 for π Aqr and 107fdg7 ± 0fdg4 for 60 Cyg,
and model the wavelength dependence of the observed polarization during
the quiescent diskless phase of each star to determine the interstellar
polarization along the line of sight. Minor outbursts observed during
the quiescent phase of each star shared similar lifetimes as those
previously reported for μ Cen, suggesting that the outbursts represent
the injection and subsequent viscous dissipation of individual blobs of
material into the inner circumstellar environments of these stars. We
also observe deviations from the mean intrinsic polarization position
angle during polarization outbursts in each star, indicating deviations
from axisymmetry. We propose that these deviations might be indicative
of the injection (and subsequent circularization) of new blobs into
the inner disk, either in the plane of the bulk of the disk material
or in a slightly inclined (non-coplanar) orbit.
Title: A White Light Megaflare on the dM4.5e Star YZ CMi
Authors: Kowalski, Adam; Hawley, S. L.; Holtzman, J. A.; Wisniewski,
J. P.; Hilton, E. J.
Bibcode: 2010AAS...21542411K
Altcode: 2010BAAS...42..332K
Due to their strong and persistent surface magnetic fields, some M
dwarfs frequently produce very explosive and energetic flares in the
optical and near-UV. However, observations and radiative hydrodynamic
simulations of flares are in stark disagreement over the type of
emission which characterizes the continuum at these wavelengths. On
January 16, 2009, we observed a white light megaflare on the dM4.5e star
YZ CMi as part of a long-term spectroscopic flare-monitoring campaign
to constrain the spectral shape of optical flare emission. This flare
was observed with simultaneous U-band photometry and 3400 A - 9000 A
spectroscopy with the NMSU 1 m and ARC 3.5 m telescopes at the Apache
Point Observatory. The event persisted for over 7.5 hours and at the
flare peak, YZ CMi's U-band flux was 5.8 magnitudes brighter than in
its quiescent state. The properties of this flare mark it as one of the
most energetic and long-lasting white light flares ever to be observed
on an isolated star. We present the detailed light curve properties and
a time-resolved spectral analysis of the continuum and emission lines
using over 160 spectra obtained during 1.3 hours of the decay phase of
the flare, during which there were complex light curve variations with
the U-band flux still elevated at 15-38 times the quiescent level. AFK, SLH, & EJH acknowledge support from NSF grant AST 0807205
JPW acknowledges support from NSF Astronomy & Astrophysics
Postdoctoral Fellowship AST 08-02230
Title: Mysterious Disturbances of Stellar "Frisbees"
Authors: Draper, Zachary H.; Wisniewski, J. P.; Bjorkman, K. S.;
Meade, M. R.; Kowalski, A. F.; Bjorkman, J. E.
Bibcode: 2010AAS...21542824D
Altcode: 2010BAAS...42..348D
Classical "Be” stars are massive, rapidly rotating stars having
gaseous circumstellar decretion disks which are known to sometimes
dissipate and regenerate. Since the mechanism for forming these disks
is not known, observing these stars when they transition between a
"Be” phase and a normal B star phase can help constrain what causes
the disks to form. We have analyzed 15 years of spectroscopic and
spectropolarimetric data from the Ritter and Pine Bluff Observatories
of two "Be” stars, 60 Cygni and Pi Aquarii, during which such a
transition phase from Be to B star occurred. The time-scale of 60
Cyg's disk loss was 1000 days, during which the disk emission declined
monotonically, while Pi Aqr's disk loss episode lasted 2440 days and was
interrupted by two major injection events of new disk material. We used
the wavelength dependence of polarization during each stars disk-less
phase to determine the interstellar polarization. Analysis of the
intrinsic polarization and H-alpha equivalent width measurements show
that both disks faded in an inside-out manner, with timescales much
longer than the orbital periods of their binary companions. We also
detect small deviations away from the overall disk position angle in
our polarization data; we speculate that this might be indicative
of either a warp in the inner disk region or the injection of new
disk material at an inclined orbit to the plane of the pre-existing
disk. We also present our initial efforts to model time dependent
behavior of our spectropolarimetric data using 3D Monte Carlo Radiative
transfer codes. JPW acknowledges support from NSF Astronomy
& Astrophysics Postdoctoral Fellowship AST 08-02230, and ZHD
acknowledges support from the UW Pre-MAP program. HPOL observations
were supported under NASA contract NAS5-26777 with University of
Wisconsin-Madison. Observations at Ritter Observatory have been
supported by the NSF under PREST grant AST 04-40784.
Title: M Dwarf Flares: Exoplanet Implications
Authors: Tofflemire, Benjamin M.; Wisniewski, J. P.; Kowalski, A. F.;
Schmidt, S. J.; Kundurthy, P.; Hawley, S. L.; Hilton, E. J.
Bibcode: 2010AAS...21542315T
Altcode: 2010BAAS...42..328T
Low mass stars such as M dwarfs are prime targets for exoplanet
transit searches as their low luminosities and small stellar radii
could enable detection of super-Earths residing in their habitable
zones. While promising targets for transit searches, M dwarfs are also
inherently variable and can exhibit up to 6 magnitude flux enhancements
in the optical U-band. This is significantly higher than the predicted
transit depths of super-Earths (0.005 magnitude flux decrease). The
behavior of flares at IR wavelengths, particularly those likely to
be used to study and characterize M dwarf exoplanets using facilities
such as JWST, remains largely unknown. To address these uncertainties,
we have executed a coordinated, contemporaneous monitoring program of
the optical and IR flux of M dwarfs known to regularly flare. A suite
of telescopes located at the Kitt Peak National Observatory and the
Apache Point Observatory were used for the observations. We present
the initial results of this program and discuss how flare events could
influence future exoplanet detection and characterization studies
in the IR. JPW acknowledges support from a NSF Astronomy and
Astrophysics Postdoctoral Fellowship, AST 08-02230.
Title: The Continued Optical to Mid-IR Evolution of V838 Monocerotis
Authors: Loebman, Sarah; Wisniewski, J. P.; Kowalski, A. F.; Barry,
R. K.; Bjorkman, K. S.; Bond, H. E.; Clampin, M.; Hammel, H. B.;
Hawley, S. L.; Lynch, D. K.; Munshi, F. A.; Russell, R. W.; Schmidt,
S. J.; Sitko, M. L.
Bibcode: 2010AAS...21543115L
Altcode: 2010BAAS...42..364L
V838 Monocerotis is an eruptive variable which gained notoriety in
2002 when it brightened by 9 magnitudes in a series of outbursts,
and eventually developed a spectacular light echo. The star's mid-IR
flux increased by a factor of 2 between 2004 and 2007, suggesting that
new dust was condensing from the expanding ejecta of the outbursts,
while more recent optical spectroscopic observations suggest that these
expanding ejecta have engulfed the system's B3V binary companion. We
present new optical, near-IR, and mid-IR spectroscopic and mid-IR
photometric observations of V838 Monocerotis obtained between 2008-2009
at the Apache Point Observatory 3.5m, NASA IRTF 3m, and Gemini South 8m
telescopes. We discuss the chemistry and continued evolution of recently
formed dust in the system in the context of previously published
photometric, spectroscopic, and spectro-polarimetric observations of
the system. This work is supported at The Aerospace Corporation
by the Independent Research and Development program; JPW acknowledges
support from a NSF Astronomy & Astrophysics Postdoctoral Fellowship,
AST 08-02230.
Title: Flares on M Dwarfs from a Time-Resolved SDSS Spectral Sample
Authors: Hilton, Eric J.; Hawley, S. L.; West, A. A.; Kowalski, A. F.
Bibcode: 2010AAS...21542410H
Altcode: 2010BAAS...42..332H
We present flare rates and analysis of individual flares using
time-resolved spectra of M dwarfs from the Sloan Digital Sky Survey
Data Release 5. Each of the 40,000 M dwarf spectra from the West et
al. (2008) DR5 sample represents a co-addition of several shorter
(9-15 min) spectra. We analyze nearly 200,000 of these short spectra,
subdividing them by spectral type and by signal-to-noise ratio and use
statistical methods to assign variability and flaring status. These
data allow us to investigate the spectroscopic time-domain properties
of low-mass stars.
Title: LSST Science Book, Version 2.0
Authors: LSST Science Collaboration; Abell, Paul A.; Allison, Julius;
Anderson, Scott F.; Andrew, John R.; Angel, J. Roger P.; Armus, Lee;
Arnett, David; Asztalos, S. J.; Axelrod, Tim S.; Bailey, Stephen;
Ballantyne, D. R.; Bankert, Justin R.; Barkhouse, Wayne A.; Barr,
Jeffrey D.; Barrientos, L. Felipe; Barth, Aaron J.; Bartlett, James
G.; Becker, Andrew C.; Becla, Jacek; Beers, Timothy C.; Bernstein,
Joseph P.; Biswas, Rahul; Blanton, Michael R.; Bloom, Joshua S.;
Bochanski, John J.; Boeshaar, Pat; Borne, Kirk D.; Bradac, Marusa;
Brandt, W. N.; Bridge, Carrie R.; Brown, Michael E.; Brunner, Robert
J.; Bullock, James S.; Burgasser, Adam J.; Burge, James H.; Burke,
David L.; Cargile, Phillip A.; Chandrasekharan, Srinivasan; Chartas,
George; Chesley, Steven R.; Chu, You-Hua; Cinabro, David; Claire,
Mark W.; Claver, Charles F.; Clowe, Douglas; Connolly, A. J.; Cook,
Kem H.; Cooke, Jeff; Cooray, Asantha; Covey, Kevin R.; Culliton,
Christopher S.; de Jong, Roelof; de Vries, Willem H.; Debattista,
Victor P.; Delgado, Francisco; Dell'Antonio, Ian P.; Dhital, Saurav;
Di Stefano, Rosanne; Dickinson, Mark; Dilday, Benjamin; Djorgovski,
S. G.; Dobler, Gregory; Donalek, Ciro; Dubois-Felsmann, Gregory;
Durech, Josef; Eliasdottir, Ardis; Eracleous, Michael; Eyer, Laurent;
Falco, Emilio E.; Fan, Xiaohui; Fassnacht, Christopher D.; Ferguson,
Harry C.; Fernandez, Yanga R.; Fields, Brian D.; Finkbeiner, Douglas;
Figueroa, Eduardo E.; Fox, Derek B.; Francke, Harold; Frank, James
S.; Frieman, Josh; Fromenteau, Sebastien; Furqan, Muhammad; Galaz,
Gaspar; Gal-Yam, A.; Garnavich, Peter; Gawiser, Eric; Geary, John;
Gee, Perry; Gibson, Robert R.; Gilmore, Kirk; Grace, Emily A.; Green,
Richard F.; Gressler, William J.; Grillmair, Carl J.; Habib, Salman;
Haggerty, J. S.; Hamuy, Mario; Harris, Alan W.; Hawley, Suzanne L.;
Heavens, Alan F.; Hebb, Leslie; Henry, Todd J.; Hileman, Edward;
Hilton, Eric J.; Hoadley, Keri; Holberg, J. B.; Holman, Matt J.;
Howell, Steve B.; Infante, Leopoldo; Ivezic, Zeljko; Jacoby, Suzanne
H.; Jain, Bhuvnesh; R; Jedicke; Jee, M. James; Garrett Jernigan,
J.; Jha, Saurabh W.; Johnston, Kathryn V.; Jones, R. Lynne; Juric,
Mario; Kaasalainen, Mikko; Styliani; Kafka; Kahn, Steven M.; Kaib,
Nathan A.; Kalirai, Jason; Kantor, Jeff; Kasliwal, Mansi M.; Keeton,
Charles R.; Kessler, Richard; Knezevic, Zoran; Kowalski, Adam;
Krabbendam, Victor L.; Krughoff, K. Simon; Kulkarni, Shrinivas;
Kuhlman, Stephen; Lacy, Mark; Lepine, Sebastien; Liang, Ming;
Lien, Amy; Lira, Paulina; Long, Knox S.; Lorenz, Suzanne; Lotz,
Jennifer M.; Lupton, R. H.; Lutz, Julie; Macri, Lucas M.; Mahabal,
Ashish A.; Mandelbaum, Rachel; Marshall, Phil; May, Morgan; McGehee,
Peregrine M.; Meadows, Brian T.; Meert, Alan; Milani, Andrea; Miller,
Christopher J.; Miller, Michelle; Mills, David; Minniti, Dante; Monet,
David; Mukadam, Anjum S.; Nakar, Ehud; Neill, Douglas R.; Newman,
Jeffrey A.; Nikolaev, Sergei; Nordby, Martin; O'Connor, Paul; Oguri,
Masamune; Oliver, John; Olivier, Scot S.; Olsen, Julia K.; Olsen,
Knut; Olszewski, Edward W.; Oluseyi, Hakeem; Padilla, Nelson D.;
Parker, Alex; Pepper, Joshua; Peterson, John R.; Petry, Catherine;
Pinto, Philip A.; Pizagno, James L.; Popescu, Bogdan; Prsa, Andrej;
Radcka, Veljko; Raddick, M. Jordan; Rasmussen, Andrew; Rau, Arne; Rho,
Jeonghee; Rhoads, James E.; Richards, Gordon T.; Ridgway, Stephen
T.; Robertson, Brant E.; Roskar, Rok; Saha, Abhijit; Sarajedini,
Ata; Scannapieco, Evan; Schalk, Terry; Schindler, Rafe; Schmidt,
Samuel; Schmidt, Sarah; Schneider, Donald P.; Schumacher, German;
Scranton, Ryan; Sebag, Jacques; Seppala, Lynn G.; Shemmer, Ohad;
Simon, Joshua D.; Sivertz, M.; Smith, Howard A.; Allyn Smith, J.;
Smith, Nathan; Spitz, Anna H.; Stanford, Adam; Stassun, Keivan G.;
Strader, Jay; Strauss, Michael A.; Stubbs, Christopher W.; Sweeney,
Donald W.; Szalay, Alex; Szkody, Paula; Takada, Masahiro; Thorman,
Paul; Trilling, David E.; Trimble, Virginia; Tyson, Anthony; Van
Berg, Richard; Vanden Berk, Daniel; VanderPlas, Jake; Verde, Licia;
Vrsnak, Bojan; Walkowicz, Lucianne M.; Wandelt, Benjamin D.; Wang,
Sheng; Wang, Yun; Warner, Michael; Wechsler, Risa H.; West, Andrew
A.; Wiecha, Oliver; Williams, Benjamin F.; Willman, Beth; Wittman,
David; Wolff, Sidney C.; Wood-Vasey, W. Michael; Wozniak, Przemek;
Young, Patrick; Zentner, Andrew; Zhan, Hu
Bibcode: 2009arXiv0912.0201L
Altcode:
A survey that can cover the sky in optical bands over wide fields to
faint magnitudes with a fast cadence will enable many of the exciting
science opportunities of the next decade. The Large Synoptic Survey
Telescope (LSST) will have an effective aperture of 6.7 meters and an
imaging camera with field of view of 9.6 deg^2, and will be devoted
to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each
pointing will be imaged 2000 times with fifteen second exposures in six
broad bands from 0.35 to 1.1 microns, to a total point-source depth
of r~27.5. The LSST Science Book describes the basic parameters of
the LSST hardware, software, and observing plans. The book discusses
educational and outreach opportunities, then goes on to describe
a broad range of science that LSST will revolutionize: mapping the
inner and outer Solar System, stellar populations in the Milky Way and
nearby galaxies, the structure of the Milky Way disk and halo and other
objects in the Local Volume, transient and variable objects both at low
and high redshift, and the properties of normal and active galaxies at
low and high redshift. It then turns to far-field cosmological topics,
exploring properties of supernovae to z~1, strong and weak lensing,
the large-scale distribution of galaxies and baryon oscillations, and
how these different probes may be combined to constrain cosmological
models and the physics of dark energy.
Title: M Dwarfs in Sloan Digital Sky Survey Stripe 82: Photometric
Light Curves and Flare Rate Analysis
Authors: Kowalski, Adam F.; Hawley, Suzanne L.; Hilton, Eric J.;
Becker, Andrew C.; West, Andrew A.; Bochanski, John J.; Sesar, Branimir
Bibcode: 2009AJ....138..633K
Altcode: 2009arXiv0906.2030K
We present a flare rate analysis of 50,130 M dwarf light curves in
Sloan Digital Sky Survey Stripe 82. We identified 271 flares using
a customized variability index to search ~2.5 million photometric
observations for flux increases in the u and g bands. Every image
of a flaring observation was examined by eye and with a point-spread
function-matching and image subtraction tool to guard against false
positives. Flaring is found to be strongly correlated with the
appearance of Hα in emission in the quiet spectrum. Of the 99 flare
stars that have spectra, we classify eight as relatively inactive. The
flaring fraction is found to increase strongly in stars with redder
colors during quiescence, which can be attributed to the increasing
flare visibility and increasing active fraction for redder stars. The
flaring fraction is strongly correlated with |Z| distance such that
most stars that flare are within 300 pc of the Galactic plane. We derive
flare u-band luminosities and find that the most luminous flares occur
on the earlier-type m dwarfs. Our best estimate of the lower limit
on the flaring rate (averaged over Stripe 82) for flares with Δu
>= 0.7 mag on stars with u < 22 is 1.3 flares hr-1
deg-2 but can vary significantly with the line of sight. Based on observations obtained with the Apache Point Observatory
3.5 m telescope, which is owned and operated by the Astrophysical
Research Consortium.
Title: M Dwarf Flares: Exoplanet Implications
Authors: Wisniewski, John; Kowalski, Adam; Schmidt, Sarah; Hawley,
Suzanne; Kundurthy, Praveen
Bibcode: 2009noao.prop..280W
Altcode:
Low mass M dwarfs are attractive stars for exoplanet transit research as
their low luminosities and small stellar radii could enable detection
of super-Earths residing in their habitable zones using existing
technology. Future IR facilities such as JWST will undoubtedly attempt
to characterize these systems through detailed transit observations. M
dwarfs can exhibit highly energetic flare events which cause <0.1
to 6.0 magnitude flux enhancements in the optical U-band, which is
significantly higher than the predicted transit depths of super- Earths
(~0.005 magnitude flux decrease). While Solar flares have been observed
to cause IR continuum enhancements (Xu et al 2006); surprisingly, it is
not known whether energetic flares associated with M dwarfs similarly
induce IR variability. We propose to contemporaneously monitor the
optical & IR flux of two M dwarfs known to regularly flare, to
determine what effect flares could have on future IR characterization
studies of M dwarf exoplanets.
Title: Short Period Variability Of An M-dwarf In SDSS Stripe-82
Authors: Munshi, Ferah; Becker, A.; Hawley, S. L.; Bochanski, J. J.;
Sesar, B.; Kowalski, A.
Bibcode: 2009AAS...21443007M
Altcode:
We present analysis of a unique short-period object selected from the
SDSS-II Stripe 82 photometric time-domain database. This object stands
out in color-period space, having the colors and spectrum of an early
M-dwarf (M0-M1) but a photometric period of 0.1 days, an amplitude of
0.2 magnitudes, and a sinusoidal lightcurve. It is unusual to find
such a red object with such a short period. We have obtained
multiple epochs of spectroscopy with the MAGE spectrograph at Magellan
to constrain any radial velocity variations. We examine the possible
interpretations of this system, including : an M-dwarf/M-dwarf
eclipsing system, which would be near the Algol limit; stellar rotation
with persistent star spots; and stellar pulsation.
Title: Contemporaneous Optical and IR Spectroscopy of Be Star
Circumstellar Disks
Authors: Hesselbach, Erica; Bjorkman, K. S.; Wisniewski, J. P.;
Kowalski, A. F.
Bibcode: 2009AAS...21430104H
Altcode:
Double-peaked hydrogen emission line profiles in classical Be stars
can be significantly asymmetric, and these asymmetries can vary in
a quasi-periodic manner with periods of several years. This has been
interpreted as evidence of one-armed density waves in the circumstellar
disks surrounding these stars. The density structure of these disks can
be explored as a function of radius by observing contemporaneously the
profile shapes of the hydrogen lines appearing in the optical and near
infrared. Observations of 33 bright Be stars monitored in the optical
at Ritter Observatory and in the near-IR using the NASA IRTF with SpeX
between September 2005 and January 2008 are presented. A range of common
Be star line profile shapes are represented, including some stars whose
asymmetric profiles are known to vary quasi-periodically. Correlations
between optical and IR hydrogen lines will be discussed and implications
for one-armed density wave models will be considered. We thank
the NASA IRTF for observing time allocations and support. We thank
the Ritter observing team, and especially Nancy Morrison, for crucial
assistance with the supporting optical observations.
Title: M Dwarf Flares from Time-Resolved SDSS Spectra
Authors: Hilton, Eric J.; Hawley, Suzanne; West, Andrew A.; Kowalski,
Adam
Bibcode: 2009AIPC.1094..652H
Altcode: 2009csss...15..652H
Flares on low-mass dwarfs are a major source of variability in
the optical and UV in the Galaxy. In addition to being a source of
optical transients, these flares may have an important effect on
the habitability of planets orbiting low-mass dwarfs. We present a
study of flares on M dwarfs determined from Sloan Digital Sky Survey
time-resolved spectra. Our sample consists of tens of thousands of M
dwarfs whose SDSS spectra were formed from co-adds of several (typically
3-5) consecutive shorter (typically 9-15 minute) exposures. We present
the Flare Line Index as a way to identify flares in these individual
component spectra with crude time-resolution, and investigate the
short-term variability of the Balmer and Ca II emission lines.
Title: Diagnosing the Structure of the HD 163296 Protoplanetary Disk
via Coronagraphic Imaging Polarimetry
Authors: Kowalski, Adam F.; Wisniewski, John P.; Clampin, Mark; Grady,
Carol A.; Sitko, Michael L.; Bjorkman, Karen S.; Fukagawa, Misato;
Hines, Dean C.; Katoh, Eri; Whitney, Barbara A.
Bibcode: 2009AIPC.1094..393K
Altcode: 2009csss...15..393K
We report our initial analysis of the H-band polarized and total
intensity of the nearby Herbig Ae star HD 163296, and characterize
the morphology of the scattered light disk in the context of previous
optical HST coronagraphic imagery. Our observations were obtained
as part of a multi-epoch campaign designed to diagnose and correlate
the behavior of the inner and outer regions of select protoplanetary
disks. This campaign will help test recent suggestions (Sitko et
al. 2008; Wisniewski et al. 2008) that the HD 163296 disk experiences
the novel phenomenon of time-variable self-shadowing, whereby occasional
changes in the scale height of the inner disk wall induce changes in
the illumination of the outer disk.
Title: Understanding Activity in Low Mass Stars
Authors: Browning, Matthew K.; Walkowicz, Lucianne M.; West, Andrew
A.; Basri, Gibor; Browning, Matthew K.; Kowalski, Adam F.; Hilton,
Eric; Bouchanski, John J.
Bibcode: 2009astro2010S..30B
Altcode:
No abstract at ADS
Title: Flare Rates on M Dwarfs: Observing Program
Authors: Hilton, Eric J.; Hawley, S.; Ule, N.; Kowalski, A.; Gomez,
T.; Grammer, S.; Holtzman, J.; Huang, M.; Huehnerhoff, J.; Morgan, D.
Bibcode: 2009AAS...21343416H
Altcode: 2009BAAS...41..305H
Determining the magnitude and rate at which low mass stars flare is
an important problem in stellar astrophysics because flares are a
major source of variability in large time domain surveys, affect the
atmospheres of orbiting planetary systems, and are manifestations
of magnetic field production and reconfiguration, processes which
are not well understood on M dwarfs. We present early results from
a multi-year observing campaign to statistically determine M dwarf
flare rates and energies as a function of spectral type and activity
level. Our observations consist of over 100 hours of monitoring M
dwarfs on three telescopes. In addition to preliminary flare rates,
we discuss our method of determining energy and duration.
Title: Multi-Epoch Coronagraphic Imaging of Herbig Ae Circumstellar
Disk Systems
Authors: Wisniewski, John P.; Clampin, M.; Grady, C. A.; Sitko, M. L.;
Bjorkman, K. S.; Kowalski, A. F.; Fukagawa, M.; Hines, D. C.; Katoh,
E.; Whitney, B. A.
Bibcode: 2009AAS...21340906W
Altcode: 2009BAAS...41..208W
We present multi-epoch coronagraphic imaging polarimetry observations
of select Herbig Ae stars, based on data obtained with UKIRT's
Imager-Spectrometer (UIST). We will focus on the HD 163296 system,
whose spatially resolved scattered light disk exhibited variability in
multi-epoch HST coronagraphic observations, possibly due to variable
self-shadowing induced by changes in the structure of the inner disk
wall (Wisniewski et al 2008; Sitko et al 2008). The morphology and
surface brightness of the scattered light disk from our 2008-epoch J-
and H-band UKIRT data will be compared against our 2007-epoch H-band
UKIRT data to further diagnose the variability of this system. J.P. Wisniewski acknowledges the support of a NSF Astronomy &
Astrophysics Postdoctoral Fellowship (0802230).
Title: M Dwarf Flare Rate Analysis of SDSS Stripe 82
Authors: Kowalski, Adam; Hawley, S. L.; Hilton, E. J.; Becker, A. C.;
Bochanski, J. J.; West, A. A.
Bibcode: 2009AAS...21343402K
Altcode: 2009BAAS...41..303K
M dwarfs produce intense flares from the X-ray to the radio,
including the optical by a physical mechanism which is still poorly
understood. Since M dwarfs comprise about 70% of the stars in the
Galaxy, their flares will be a significant source of optical transients
in future time domain surveys, such as LSST, Pan-STARRS, and GAIA. Using
a Flare Index to select flaring events from 40,000 low-cadence M dwarf
light curves, we present the flaring rate as a function of intrinsic
stellar properties, such as spectral type, level of magnetic activity,
and distance from the Galactic plane. We also discuss our results
in light of our understanding of flare physics and how our derived
flaring rates and luminosities compare to the Lacy, Moffett, &
Evans (1976) classical study of nearby active flare stars.
Title: The size distributions of asteroid families in the SDSS Moving
Object Catalog 4
Authors: Parker, A.; Ivezić, Ž.; Jurić, M.; Lupton, R.; Sekora,
M. D.; Kowalski, A.
Bibcode: 2008Icar..198..138P
Altcode: 2008arXiv0807.3762P
Asteroid families, traditionally defined as clusters of objects in
orbital parameter space, often have distinctive optical colors. We
show that the separation of family members from background interlopers
can be improved with the aid of SDSS colors as a qualifier for family
membership. Based on an ∼88,000 object subset of the Sloan Digital Sky
Survey Moving Object Catalog 4 with available proper orbital elements,
we define 37 statistically robust asteroid families with at least 100
members (12 families have over 1000 members) using a simple Gaussian
distribution model in both orbital and color space. The interloper
rejection rate based on colors is typically ∼10% for a given orbital
family definition, with four families that can be reliably isolated
only with the aid of colors. About 50% of all objects in this data
set belong to families, and this fraction varies from about 35% for
objects brighter than an H magnitude of 13 and rises to 60% for objects
fainter than this. The fraction of C-type objects in families decreases
with increasing H magnitude for H>13, while the fraction of S-type
objects above this limit remains effectively constant. This suggests
that S-type objects require a shorter timescale for equilibrating the
background and family size distributions via collisional processing. The
size distribution varies significantly among families, and is typically
different from size distributions for background populations. The
size distributions for 15 families display a well-defined change of
slope and can be modeled as a "broken" double power-law. Such "broken"
size distributions are twice as likely for S-type familes than for
C-type families (73% vs. 36%), and are dominated by dynamically old
families. The remaining families with size distributions that can be
modeled as a single power law are dominated by young families (<1
Gyr). When size distribution requires a double power-law model, the
two slopes are correlated and are steeper for S-type families. No
such slope-color correlation is discernible for families whose size
distribution follows a single power law. For several very populous
families, we find that the size distribution varies with the distance
from the core in orbital-color space, such that small objects are more
prevalent in the family outskirts. This "size sorting" is consistent
with predictions based on the Yarkovsky effect.
Title: First Science Results from the UKIRT UIST Coronagraphic
Imaging Polarimeter
Authors: Wisniewski, John P.; Kowalski, A. F.; Clampin, M.; Grady,
C. A.; Sitko, M. L.; Bjorkman, K. S.; Hines, D. C.; Whitney, B. A.
Bibcode: 2007AAS...211.5010W
Altcode: 2007BAAS...39..813W
We present the first science results from the newly commissioned
coronagraphic imaging polarimetry mode of UKIRT's Imager-Spectrometer
(UIST). Our pilot science program is designed to begin to trace
the evolution of the spatial and size distribution of dust grains
in protoplanetary disk systems. The initial observations obtained
as part of this program, at H-band, have spatially resolved the
scattered light disk associated with a nearby Herbig Ae star. We
characterize the morphology of the disk in our H-band coronagraphic
imaging polarimetry observations, compare these results to archival
optical HST coronagraphic imagery, and discuss the possible origins
of morphological structures seen in these data. J.P. Wisniewski
acknowledges the support of a NPP Fellowship at NASA GSFC, via award
NNH06CC03B.
Title: Galactic M Dwarf Flare Rates
Authors: Hawley, Suzanne L.; Hilton, E. J.; Kowalski, A. F.; Bochanski,
J. J.; West, A. A.
Bibcode: 2007AAS...21110306H
Altcode: 2007BAAS...39..920H
We present preliminary results from our effort to model M dwarf flare
rates in the Galaxy. Using existing flare data and new determinations of
the M dwarf luminosity function and activity fractions from SDSS data,
we have developed numerical simulations to model the number of flares
seen along a given Galactic sightline. We compare the simulations with
data from the SDSS repeat scans obtained in the equatorial region. These
simulations will be useful for predicting the detection of M dwarf
variability in new time domain surveys such as PanSTARRs and LSST. Based on data from the Sloan Digital Sky Survey (www.sdss.org)
Title: Toward Mapping the Detailed Density Structure of Classical
Be Circumstellar Disks
Authors: Wisniewski, J. P.; Kowalski, A. F.; Bjorkman, K. S.; Bjorkman,
J. E.
Bibcode: 2007ASPC..361..524W
Altcode:
We present the preliminary results of near contemporaneous optical and
infrared spectroscopic observations of selected classical Be stars. We
find strong evidence of oppositely oriented V/R hydrogen line profiles
in the optical versus infrared spectra of ζ Tau, and briefly discuss
how sustained contemporaneous optical and infrared spectroscopic
observations might enable us to trace the detailed density structure
of classical Be circumstellar disks.
Title: Toward Mapping the Detailed Density Structure of Classical
Be Circumstellar Disks
Authors: Wisniewski, J. P.; Kowalski, A. F.; Bjorkman, K. S.; Bjorkman,
J. E.; Carciofi, A. C.
Bibcode: 2007ApJ...656L..21W
Altcode: 2007astro.ph..1010W
The first results from a near-contemporaneous optical and infrared
spectroscopic observing program designed to probe the detailed density
structure of classical Be circumstellar disks are presented. We report
the discovery of asymmetrical infrared emission lines of He I, O I,
Fe II, and the Brackett, Paschen, and Pfund series lines of H I that
exhibit an opposite V/R orientation (V>R) to that observed for
the optical Balmer Hα line (V<R) in the classical Be star ζ
Tau. We interpret these data as evidence that the density wave that
characterizes ζ Tau's disk has a significantly different average
azimuthal morphology in the inner disk region as compared to the outer
disk region. A follow-up multiwavelength observational campaign to trace
the temporal evolution of these line profile morphologies, along with
detailed theoretical modeling, is suggested to test this hypothesis.
Title: Flare Rate Analysis of M-Dwarf Lightcurves
Authors: Kowalski, Adam F.; Hilton, E. J.; Becker, A. C.; Hawley, S. L.
Bibcode: 2006AAS...209.8907K
Altcode: 2006BAAS...38.1025K
We present a preliminary variability index analysis of lightcurves of
several thousand M-dwarfs extracted from the Sloan Digital Sky Survey
Equatorial Stripe. These objects have been subclassed by magnetic
activity and spectral type. This analysis will provide the rates of
flaring activity as a function of the above parameters as well as
characterizing the colors of these stars while active. M-dwarf flare
rates will be applicable to next-generation time domain surveys such
as the Large Synoptic Survey Telescope by predicting the fraction
of observed variable objects that are flaring M-dwarfs and not other
cosmological transients.
Title: Circumstellar Disks in the IR: Identification of New Systems
and Evidence of Complex Density Structures
Authors: Wisniewski, J. P.; Kowalski, A. F.; Bjorkman, K. S.; Bjorkman,
J. E.
Bibcode: 2005AAS...206.0803W
Altcode: 2005BAAS...37Q.440W
We use 0.8-2.4 micron spectroscopy to explore the circumstellar
environments of a small sample of stars in the Galactic clusters
NGC 2186 and NGC 2439 that were previously identified as excess Hα
emitters from 2-color diagram photometric observations. We detect
both H I and various metal emission lines in ∼60% of our sample,
indicating that these objects do have circumstellar disks. Analysis of
line profile morphologies suggests the presence of a one-armed spiral
density wave in at least one circumstellar disk system. Furthermore,
we find the V/R ratios of the H I Brackett emission lines are opposite
those of the Fe II emission lines in this particular system, implying
that our observations may be used to probe the structure of the spiral
density wave as a function of disk radius. We also present
initial results of near contemporaneous optical and 0.8-2.4 micron
spectroscopic observations of several known Galactic classical Be
stars. Theoretical line profile calculations (Waters & Marlborough
1992) predict scenarios in which one should observe the V/R ratios of
the optical Hα and IR H lines to be oppositely oriented; we believe
we have found conclusive evidence of this in our observations of Zeta
Tau. We discuss our efforts to use these line strengths and profiles
to constrain the density structure and fundamental parameters of these
circumstellar disks. Observations were obtained using the SpeX
instrument at the NASA IRTF on Mauna Kea, Hawaii. This work has been
supported in part by grants from the NASA LTSA, NASA GSRP, Sigma Xi
GIAR, and NSF REU programs. KSB is a Cottrell Scholar of the Research
Corporation and gratefully acknowledges their support.
Title: Quantitative indicator for semiquantum chaos
Authors: Kowalski, A. M.; Martin, M. T.; Nuñez, J.; Plastino, A.;
Proto, A. N.
Bibcode: 1998PhRvA..58.2596K
Altcode:
By generalizing to a mixed-state environment the treatment recently
given to a model advanced by Cooper et al. [Phys. Rev. Lett. 72, 1337
(1994)], we show that some characteristics of the so-called semiquantum
chaos can be described by recourse to a special motion invariant of
the problem, that thus becomes a chaos indicator.