Abstract
Abstract 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.
Highlights
Stellar flares are a common phenomenon around M dwarfs
We present observations and analysis of high resolution NIR spectra of vB 10, which were obtained with Habitable zone Planet Finder (HPF) on the 10 m Hobby Eberly Telescope (HET), where a stellar flare was serendipitously detected
We present observations of a flare around the ultracool M8 dwarf vB 10, which include high resolution NIR spectra from HPF, as well as photometry from the acquisition camera (ACAM) on HET
Summary
Stellar flares are a common phenomenon around M dwarfs. These transient events take place when magnetic field lines reconnect in the upper atmosphere of the star. High resolving power (R ∼ 110, 000) spectra were obtained for the M7 dwarf vB 8 by Martın (1999) covering a bandpass spanning about 5400 ̊A – 10600 ̊A These observations showed the rise and fall of the He I D3 line as well as the Na I doublet during the flare of this cool dwarf. Crespo-Chacon et al (2006) obtained medium resolution optical spectra (3500 ̊A – 7200 ̊A) for the active M3 star AD Leo to study the chromospheric lines during multiple flares. Fuhrmeister et al (2008) studied a flare around the M5.5 dwarf CN Leo using observations spanning 3000 ̊A – 10500 ̊A, at R ∼ 40, 000 These observations identified not just a range of chromospheric lines in emission, and continuum enhancement and line asymmetry. Space Telescope (HST ). Fleming et al (2000) first reported an X ray flare from vB 10, whereas Berger et al (2008) conducted simultaneous X-ray, UV, and optical observations and observed several flares on vB 10
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