mid-M Dwarf Research Articles

HD 207651: A Triple System with Scuti and Ellipsoidal Variations But No Doradus Pulsations

We examine HD 207651 as a possible example of a star exhibiting both γ Doradus and δ Scuti type pulsations. We find photometric periods of 0.06479 and 0.06337 days with peak-to-peak amplitudes in Johnson B of 21 and 13 mmag, respectively, clearly indicating δ Scuti pulsations. Additional light variation with a period of 0.73540 days and an even larger amplitude of 31 mmag is within the range of γ Doradus pulsation periods but results instead from the ellipticity effect. HD 207651 has a composite spectrum with a weak, narrow absorption line superposed near the center of each broad metal line. The broad-lined component is the primary of a short-period, single-lined binary, which has a period of 1.4708 days, twice the period of the ellipsoidal variations seen in the photometry. We determine the primary to be an A8 giant and estimate the unseen secondary of the short-period binary to be a mid-M dwarf. The narrow-lined star, an F7: dwarf, shows velocity variability with a period of months or perhaps years. It is thus a more distant companion to the binary, making HD 207651 a triple system. All light variations come from the A8 giant primary star. Since the 0.73540 day variation results from the ellipticity effect, HD 207651 is not an example of a star that exhibits both δ Scuti and γ Doradus pulsations. The growing number of confirmed γ Doradus stars that also occur within the δ Scuti instability strip but fail to show additional δ Scuti variability makes it increasingly unlikely that the two types of pulsation can coexist in the same star.

JHK photometry of WD 0950+139

view Abstract Citations (19) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS JHK Photometry of WD 0950+139 Fulbright, Michael S. ; Liebert, James Abstract We present results from several nights of JHK photometry of the hot DA white dwarf 0950+139. It has a significant infrared excess over the expected flux from the white dwarf alone, confirming a previous finding by Zuckerman et al. (1991). The infrared excess corresponds to an upper limit on the spectral type of a companion of M4 V. We consider two models for the infrared excess of 0950+139, involving either a mid-M dwarf or a substellar object as a close companion. If 0950+139 is a close binary with a period of days, we predict that we should detect variation in the infrared fluxes due to reprocessing by the companion. Such variation was not detected, which may mean the system has a different orbital period or an inclination near 0 deg. Publication: The Astrophysical Journal Pub Date: June 1993 DOI: 10.1086/172743 Bibcode: 1993ApJ...410..275F Keywords: Binary Stars; M Stars; Stellar Spectrophotometry; White Dwarf Stars; Spectral Energy Distribution; Stellar Models; Stellar Orbits; Astrophysics; STARS: BINARIES: GENERAL; STARS: INDIVIDUAL ALPHANUMERIC: WD 0950; 139; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (1)

Detection of a BY Draconis-like binary companion to contact binary XY Leonis

view Abstract Citations (36) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of a BY Draconis--like Binary Companion to the Contact Binary XY Leonis Barden, Samuel C. Abstract Spectroscopic observations are presented which reveal the presence of the previously suspected companion of the well-known W UMa binary, XY Leo. This companion is deduced to be a BY Draconis binary composed of late-K to mid-M dwarf stars with an orbital period of 0.d805. The Hα emission features presented here arise from the BY Draconis component, not from the contact binary. The Ca II H and K emission features reported by previous investigators to be attributable to the more massive W UMa component are, instead, associated with the components of the BY Draconis binary. This finding has obvious implications on the use of XY Leonis in the study of the chromospheric activity relations among close binary systems. Either high-resolution spectroscopy (λ/Δλ > 10,000) or high spatial resolution imaging (< 0."1) will be required to properly disentangle the chromospheric and coronal emission arising from each binary component. Once proper observation and deconvolution is possible XY Leonis should prove to be valuable for such studies, given the equal ages and chemical compositions of the two binaries, and since the masses and inclinations for each component will be well determined for this system as soon as the astrometric orbit is measured. In the present study, self-consistent arguments suggest non-coplanarity in the orbits. Publication: The Astrophysical Journal Pub Date: June 1987 DOI: 10.1086/165280 Bibcode: 1987ApJ...317..333B Keywords: Companion Stars; Eclipsing Binary Stars; Stellar Orbits; Stellar Spectra; Dwarf Stars; Emission Spectra; M Stars; Stellar Physics; Stellar Systems; Astronomy; CA II EMISSION; STARS: ECLIPSING BINARIES; STARS: INDIVIDUAL CONSTELLATION NAME: XY LEONIS full text sources ADS | data products SIMBAD (2)