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<!DOCTYPE html>
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<strong>Sarah Jane Schmidt</strong>
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<h1 class="post-title">publications</h1>
<h5 class="post-description">refereed publications generated by jekyll-scholar and <a href="https://ui.adsabs.harvard.edu/user/libraries/i8xalhGwSJKpbZlp7RmcIg">my ads library</a></h5>
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<article class="post-content publications clearfix">
<h3 class="year">2021</h3>
<ol class="bibliography"><li>
<div id="2021A&A...645A..42I">
<span class="title">Flares in open clusters with K2. II. Pleiades, Hyades, Praesepe, Ruprecht 147, and M 67</span>
<span class="author">
Ilin, Ekaterina,
<em>Schmidt, Sarah J.</em>,
Poppenhäger, Katja,
Davenport, James R. A.,
Kristiansen, Martti H.,
and
Omohundro, Mark
</span>
<span class="periodical">
<em>A&A</em>
2021
</span>
<span class="links">
[<a href="https://ui.adsabs.harvard.edu/abs/2021A&A...645A..42I" target="_blank">ADS</a>]
[<a href="http://arxiv.org/abs/2010.05576" target="_blank">arXiv</a>]
[<a class="abstract">Abstract</a>]
</span>
<!-- Hidden abstract block -->
<span class="abstract hidden">
<p>Context. Magnetic fields are a key component in the main sequence evolution of low mass stars. Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. The occurrence rates and energy distributions of flares trace stellar characteristics such as mass and age. However, before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration.
Aims: This work sets out to quantify the flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite.
Methods: Drawing from the complete K2 archive, we searched 3435 ∼80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates.
Results: We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6 Gyr (M 67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690 Myr) to the sample as a comparison cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with exponent α ≈ 1.84−2.39.
Conclusions: We confirm that flaring rates decline with age, and decline faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We find evidence that a rapid decline in flaring activity occurred in M1─M2 dwarfs around the ages of the Hyades and Praesepe, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates and lower mass stars still resided in the saturated activity regime. We conclude that some discrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may point to the limitations of using rotation as an age indicator without additional constraints from stellar activity.</p>
</span>
</div>
</li></ol>
<h3 class="year">2020</h3>
<ol class="bibliography"><li>
<div id="2020MNRAS.494.5751P">
<span class="title">K2 Ultracool Dwarfs Survey - VI. White light superflares observed on an L5 dwarf and flare rates of L dwarfs</span>
<span class="author">
Paudel, R. R.,
Gizis, J. E.,
Mullan, D. J.,
<em>Schmidt, S. J.</em>,
Burgasser, A. J.,
and
Williams, P. K. G.
</span>
<span class="periodical">
<em>MNRAS</em>
2020
</span>
<span class="links">
[<a href="https://ui.adsabs.harvard.edu/abs/2020MNRAS.494.5751P" target="_blank">ADS</a>]
[<a href="http://arxiv.org/abs/2004.10579" target="_blank">arXiv</a>]
[<a class="abstract">Abstract</a>]
</span>
<!-- Hidden abstract block -->
<span class="abstract hidden">
<p>Kepler, K2 long cadence data are used to study white light flares in
a sample of 45 L dwarfs. We identified 11 flares on 9 L dwarfs
with equivalent durations of (1.3-198) h and total
(UV/optical/IR) energies of ≥0.9 x
10<sup>32</sup> erg. Two superflares with energies of
>10<sup>33</sup> erg were detected on an L5 dwarf (VVV BD001):
this is the coolest object so far on which flares have been
identified. The larger superflare on this L5 dwarf has an energy
of 4.6 x10<sup>34</sup> erg and an amplitude of >300
times the photospheric level: so far, this is the largest
amplitude flare detected by the Kepler/K2 mission. The next
coolest star on which we identified a flare was an L2 dwarf:
2MASS J08585891+1804463. Combining the energies of all the
flares which we have identified on 9 L dwarfs with the total
observation time which was dedicated by Kepler to all 45 L
dwarfs, we construct a composite flare frequency distribution
(FFD). The FFD slope is quite shallow (-0.51±0.17), consistent with earlier results reported by Paudel et al.
for one particular L0 dwarf, for which the FFD slope was found
to be -0.34. Using the composite FFD, we predict that, in early-
and mid-L dwarfs, a superflare of energy 10<sup>33</sup> erg occurs
every 2.4 yr and a superflare of energy 10<sup>34</sup> erg occurs
every 7.9 yr. Analysis of our L dwarf flares suggests that
magnetic fields of ≥0.13-1.3 kG are present on
the stellar surface: such fields could suppress Type II radio
bursts.</p>
</span>
</div>
</li>
<li>
<div id="2020ApJ...892..144R">
<span class="title">A Catalog of M-dwarf Flares with ASAS-SN</span>
<span class="author">
Rodrı́guez Martı́nez, Romy,
Lopez, Laura A.,
Shappee, Benjamin J.,
<em>Schmidt, Sarah J.</em>,
Jayasinghe, Tharindu,
Kochanek, Christopher S.,
Auchettl, Katie,
and
Holoien, Thomas W. -S.
</span>
<span class="periodical">
<em>ApJ</em>
2020
</span>
<span class="links">
[<a href="https://ui.adsabs.harvard.edu/abs/2020ApJ...892..144R" target="_blank">ADS</a>]
[<a href="http://arxiv.org/abs/1912.05549" target="_blank">arXiv</a>]
[<a class="abstract">Abstract</a>]
</span>
<!-- Hidden abstract block -->
<span class="abstract hidden">
<p>We analyzed the light curves of 1376 early-to-late, nearby M dwarfs to
search for white-light flares using photometry from the All-Sky
Automated Survey for Supernovae. We identified 480 M dwarfs with
at least one potential flare employing a simple statistical
algorithm that searches for sudden increases in V-band flux.
After more detailed evaluation, we identified 62 individual
flares on 62 stars. The event amplitudes range from 0.12 <
ΔV<2.04 mag. Using classical flare
models, we place lower limits on the flare energies and obtain
V-band energies spanning 2.0x10<sup>30</sup>
≲ E<sub>V</sub> ≲
6.9x10<sup>35</sup> erg. The fraction of flaring stars
increases with spectral type, and most flaring stars show
moderate to strong Hα emission.
Additionally, we find that 14 of the 62 flaring stars are
rotational variables, and they have shorter rotation periods and
stronger Hα emission than nonflaring
rotational variable M dwarfs.</p>
</span>
</div>
</li></ol>
<h3 class="year">2019</h3>
<ol class="bibliography"><li>
<div id="2019ApJ...883..205B">
<span class="title">The Ultracool SpeXtroscopic Survey. I. Volume-limited Spectroscopic Sample and Luminosity Function of M7-L5 Ultracool Dwarfs</span>
<span class="author">
Bardalez Gagliuffi, Daniella C.,
Burgasser, Adam J.,
<em>Schmidt, Sarah J.</em>,
Theissen, Christopher,
Gagné, Jonathan,
Gillon, Michael,
Sahlmann, Johannes,
Faherty, Jacqueline K.,
Gelino, Christopher,
Cruz, Kelle L.,
Skrzypek, Nathalie,
and
Looper, Dagny
</span>
<span class="periodical">
<em>ApJ</em>
2019
</span>
<span class="links">
[<a href="https://ui.adsabs.harvard.edu/abs/2019ApJ...883..205B" target="_blank">ADS</a>]
[<a href="http://arxiv.org/abs/1906.04166" target="_blank">arXiv</a>]
[<a class="abstract">Abstract</a>]
</span>
<!-- Hidden abstract block -->
<span class="abstract hidden">
<p>We present a volume-limited, spectroscopically verified sample of M7−L5 ultracool dwarfs (UCDs) within 25 pc. The sample contains 410 sources, of which 93% have trigonometric distance measurements (80% from Gaia DR2) and 81% have low-resolution (R ∼ 120), near-infrared (NIR) spectroscopy. We also present an additional list of 60 sources that may be M7−L5 dwarfs within 25 pc when distance or spectral-type uncertainties are taken into account. The spectra provide NIR spectral and gravity classifications, and we use these to identify young sources, red and blue J − K S color outliers, and spectral binaries. We measure very low gravity and intermediate-gravity fractions of 2.1<sub>-0.8%</sub><sup>+0.9%</sup> and 7.8<sub>-1.5%</sub><sup>+1.7%</sup> , respectively; fractions of red and blue color outliers of 1.4<sub>-0.5%</sub><sup>+0.6%</sup> and 3.6<sub>-0.9%</sub><sup>+1.0%</sup> , respectively; and a spectral binary fraction of 1.6<sub>-0.5%</sub> <sup>+0.5%</sup> . We present an updated luminosity function for M7−L5 dwarfs continuous across the hydrogen-burning limit that agrees with previous studies. We estimate our completeness to range between 69% and 80% when compared to an isotropic model. However, we find that the literature late-M sample is severely incomplete compared to L dwarfs, with completeness of 62<sub>-7%</sub> <sup>+8%</sup> and 83<sub>-9%</sub> <sup>+10%</sup> , respectively. This incompleteness can be addressed with astrometric-based searches of UCDs with Gaia to identify objects previously missed by color- and magnitude-limited surveys.</p>
</span>
</div>
</li>
<li>
<div id="2019MNRAS.486.1438P">
<span class="title">K2 Ultracool Dwarfs Survey - V. High superflare rates on rapidly rotating late-M dwarfs</span>
<span class="author">
Paudel, R. R.,
Gizis, J. E.,
Mullan, D. J.,
<em>Schmidt, S. J.</em>,
Burgasser, A. J.,
Williams, P. K. G.,
Youngblood, A.,
and
Stassun, K. G.
</span>
<span class="periodical">
<em>MNRAS</em>
2019
</span>
<span class="links">
[<a href="https://ui.adsabs.harvard.edu/abs/2019MNRAS.486.1438P" target="_blank">ADS</a>]
[<a href="http://arxiv.org/abs/1812.07631" target="_blank">arXiv</a>]
[<a class="abstract">Abstract</a>]
</span>
<!-- Hidden abstract block -->
<span class="abstract hidden">
<p>We observed strong superflares (defined as flares with energy in excess of 1033 erg) on three late-M dwarfs: 2MASS J08315742+2042213 (hereafter 2M0831+2042; M7 V), 2MASS J08371832+2050349 (hereafter 2M0837+2050; M8 V), and 2MASS J08312608+2244586 (hereafter 2M0831+2244; M9 V). 2M0831+2042 and 2M0837+2050 are members of the young (700 Myr) open cluster Praesepe. The strong superflare on 2M0831+2042 has an equivalent duration (ED) of 13.7 h and an estimated energy of 1.3 × 10<sup>35</sup> erg. We observed five superflares on 2M0837+2050, on which the strongest superflare has an ED of 46.4 h and an estimated energy of 3.5 × 10<sup>35</sup> erg. This energy is larger by 2.7 orders of magnitude than the largest flare observed on the older (7.6 Gyr) planet-hosting M8 dwarf TRAPPIST-1. Furthermore, we also observed five superflares on 2M0831+2244 which is probably a field star. The estimated energy of the strongest superflare on 2M0831+2244 is 6.1 × 10<sup>34</sup> erg. 2M0831+2042, 2M0837+2050, and 2M0831+2244 have rotation periods of 0.556 ± 0.002, 0.193 ± 0.000, and 0.292 ± 0.001 d, respectively, which we measured by using K2 light curves. We compare the flares of younger targets with those of TRAPPIST-1 and discuss the possible impacts of such flares on planets in the habitable zone of late-M dwarfs.</p>
</span>
</div>
</li>
<li>
<div id="2019AJ....157..231K">
<span class="title">Exploring the Age-dependent Properties of M and L Dwarfs Using Gaia and SDSS</span>
<span class="author">
Kiman, Rocio,
<em>Schmidt, Sarah J.</em>,
Angus, Ruth,
Cruz, Kelle L.,
Faherty, Jacqueline K.,
and
Rice, Emily
</span>
<span class="periodical">
<em>AJ</em>
2019
</span>
<span class="links">
[<a href="https://ui.adsabs.harvard.edu/abs/2019AJ....157..231K" target="_blank">ADS</a>]
[<a href="http://arxiv.org/abs/1904.05911" target="_blank">arXiv</a>]
[<a class="abstract">Abstract</a>]
</span>
<!-- Hidden abstract block -->
<span class="abstract hidden">
<p>We present a sample of 74,216 M and L dwarfs constructed from two existing catalogs of cool dwarfs spectroscopically identified in the Sloan Digital Sky Survey (SDSS). We cross-matched the SDSS catalog with Gaia DR2 to obtain parallaxes and proper motions and modified the quality cuts suggested by the Gaia Collaboration to make them suitable for late-M and L dwarfs. We also provide relations between Gaia colors and absolute magnitudes with spectral type and conclude that (G − G<sub>RP</sub>) has the tightest relation to spectral type for M and L dwarfs. In addition, we study magnetic activity as a function of position on the color─magnitude diagram, finding that Hα magnetically active stars have, on average, redder colors and/or brighter magnitudes than inactive stars. This effect cannot be explained by youth alone and might indicate that active stars are magnetically inflated, binaries, and/or high metallicity. Moreover, we find that vertical velocity and vertical action dispersion are correlated with Hα emission, confirming that these two parameters are age indicators. We also find that stars below the main sequence have high tangential velocity, which is consistent with a low metallicity and old population of stars that belong to the halo or thick disk. </p>
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<div id="2019ApJ...876..115S">
<span class="title">The Largest M Dwarf Flares from ASAS-SN</span>
<span class="author">
<em>Schmidt, Sarah J.</em>,
Shappee, Benjamin J.,
van Saders, Jennifer L.,
Stanek, K. Z.,
Brown, Jonathan S.,
Kochanek, C. S.,
Dong, Subo,
Drout, Maria R.,
Frank, Stephan,
Holoien, T. W. -S.,
Johnson, Sean,