Browsing by Author "Hawley, Suzanne L."
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Item Apache Point Observatory (APO)/SMARTS Flare Star Campaign Observations. I. Blue Wing Asymmetries in Chromospheric Lines during Mid-M-Dwarf Flares from Simultaneous Spectroscopic and Photometric Observation Data(AAS) Notsu, Yuta; Kowalski, Adam F.; Maehara, Hiroyuki; Namekata, Kosuke; Hamaguchi, Kenji; Enoto, Teruaki; Tristan, Isaiah I.; Hawley, Suzanne L.; Davenport, James R. A.; Honda, Satoshi; Ikuta, Kai; Inoue, Shun; Namizaki, Keiichi; Nogami, Daisaku; Shibata, KazunariWe conducted the time-resolved simultaneous optical spectroscopic and photometric observations of mid-M-dwarf flare stars YZ CMi, EV Lac, and AD Leo. Spectroscopic observations were obtained using Apache Point Observatory 3.5 m and Small and Moderate Aperture Research Telescope System 1.5 m telescopes during 31 nights. Among the 41 detected flares, seven flares showed clear blue wing asymmetries in the Hα line, with various correspondences in flare properties. The duration of the blue wing asymmetries range from 20 minutes to 2.5 hr, including a flare showing the shift from blue to red wing asymmetry. Blue wing asymmetries can be observed during both white-light and candidate non-white-light flares. All of the seven flares showed blue wing asymmetries also in the Hβ line, but there are large varieties on which other chromospheric lines showed blue wing asymmetries. One among the 7 flares was also observed with soft X-ray spectroscopy, which enabled us to estimate the flare magnetic field and length of the flare loop. The line-of-sight velocities of the blueshifted components range from –73 to –122 km s⁻¹. Assuming that the blueshifts were caused by prominence eruptions, the mass of upward-moving plasma was estimated to be 10¹⁵–10¹⁹ g, which are roughly on the relation between flare energy and erupting mass expected from solar coronal mass ejections (CMEs). Although further investigations are necessary for understanding the observed various properties, these possible prominence eruptions on M-dwarfs could evolve into CMEs, assuming the similar acceleration mechanism with solar eruptions.Item STEADY AND TRANSIENT RADIO EMISSION FROM ULTRACOOL DWARFS(IOP, 2009-07-16) Osten, Rachel A.; Phan-Bao, N.; Hawley, Suzanne L.; Reid, I. Neill; Ojha, RoopeshWe present the results of multi-frequency radio observing campaigns designed to elucidate the nature of radio emission from very low mass stars. We detect radio emission in an additional two epochs of the ultracool dwarf binary LP 349–25, finding that the observed emission is broad band and steady on timescales between 10 s and 10.7 hr, as well as on timescales of 0.6 and 1.6 years. This system is unusual for ultracool dwarfs with detectable radio emission, in exhibiting a lack of any large-scale variability, particularly the bursting (periodic or aperiodic) behavior exhibited by the other objects with detectable levels of radio emission. We explore the constraints that the lack of variability on long- and short-timescales, and flat spectral index, imply about the radio-emitting structures and mechanism. The temporal constraints argue for a high latitude emitting region with a large inclination so that it is always in view, and survives for at least 0.6 years. Temporal constraints also limit the plasma conditions, implying that the electron density be nₑ < 4 × 10⁵ cm⁻³ and B< 130 G in order not to see time variations due to collisional or radiative losses from high-energy particles. The observations and constraints provided by them are most compatible with a nonthermal radio emission mechanism, likely gyrosynchrotron emission from a spatially homogeneous or inhomogeneous source. This indicates that, similar to behaviors noted for chromospheric, transition region, and coronal plasmas in ultracool dwarfs, the magnetic activity patterns observed in active higher mass stars can survive to the substellar boundary. We also present new epochs of multi-frequency radio observations for the ultracool dwarfs 2MASS 05233822–140322 and 2MASS14563831–2809473(=LHS 3003); each has been detected in at least one previous epoch but are not detected in the epochs reported here. The results here suggest that magnetic configurations in ultracool dwarfs can be long-lasting, and support the need for further radio monitoring using a simultaneous, multi-frequency observing approach.