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Register a new userDiscovery of a new PG1159 (GW Vir) Pulsator
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We report the discovery of pulsations in the spectroscopic PG 1159 type pre-white dwarf SDSS J075415.12+085232.18. Analysis of the spectrum by Werner, Rauch and Kepler (2014) indicated Teff=120 000+/-10 000 K, log g=7.0+/-0.3, mass M=0.52+/-0.02 Msun, C/He=0.33 by number. We obtained time-series images with the SOAR 4.1 m telescope and 2.1 m Otto Struve telescope at McDonald Observatory and show the star is also a variable PG 1159 type star, with dominant period of 525 s.
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In this paper, we present the observations of two new GW Vir stars from the extended textit{TESS} mission in both 120,s short-cadence and 20,s ultra-short-cadence mode of two pre-white dwarf stars showing hydrogen deficiency. We performed an asteroseismological analysis of these stars on the basis of PG~1159 evolutionary models that take into account the complete evolution of the progenitor stars. We searched for patterns of uniform period spacings in order to constrain the stellar mass of the stars, and employed the individual observed periods to search for a representative seismological model. The analysis of the {it TESS} light curves of TIC,333432673 and TIC,095332541 reveals the presence of several oscillations with periods ranging from 350 to 500~s associated to typical gravity ($g$)-modes. From follow-up ground-based spectroscopy, we find that both stars have similar effective temperature ($T_mathrm{eff} = 120,000 pm 10,000$,K) and surface gravity ($log g = 7.5 pm 0.5$) but a different He/C composition. On the basis of PG~1159 evolutionary tracks, we derived a spectroscopic mass of $M_{star}$ = $0.58^{+0.16}_{-0.08},M_{odot}$ for both stars. Our asteroseismological analysis of TIC,333432673 allowed us to find a constant period spacing compatible with a stellar mass $M_{star}sim 0.60-0.61,M_{odot}$, and an asteroseismological model for this star with a stellar mass $M_{star}$ = $0.589pm 0.020$ $M_{odot}$, and a seismological distance of $d= 459^{+188}_{-156}$ pc. For this star, we find an excellent agreement between the different methods to infer the stellar mass, and also between the seismological distance and that measured with {it Gaia} ($d_{rm Gaia}= 389^{+5.6}_{-5.2}$ pc). For TIC,095332541, we have found a possible period spacing that suggests a stellar mass of $M_{star}sim 0.55-0.57,M_{odot}$.
GW Vir variables are the pulsating members in the spectroscopic class of PG 1159 stars. In order to understand the characteristic differences between pulsating and non-pulsating PG 1159 stars, we analyse FUSE spectra of eleven objects, of which six are pulsating, by means of state-of-the-art NLTE model atmospheres. The numerous metal lines in the FUV spectra of these stars allow a precise determination of the photospheric parameters. We present here preliminary results of our analysis.
HD 156424 (B2 V) is a little-studied magnetic hot star in the Sco OB4 association, previously noted to display both high-frequency radial velocity (RV) variability and magnetospheric H$alpha$ emission. We have analysed the TESS light curve, and find that it is a $beta$ Cep pulsator with 11 detectable frequencies, 4 of which are independent $p$-modes. The strongest frequency is also detectable in RVs from ground-based high-resolution spectroscopy. RVs also show a long-term variation, suggestive of orbital motion with a period of $sim$years; significant differences in the frequencies determined from TESS and RV datasets are consistent with a light-time effect from orbital motion. Close examination of the stars spectrum reveals the presence of a spectroscopic companion, however as its RV is not variable it cannot be responsible for the orbital motion and we therefore infer that the system is a hierarchical triple with a so-far undetected third star. Reanalysis of LSD profiles from ESPaDOnS and HARPSpol spectropolarimetry reveals the surprising presence of a strong magnetic field in the companion star, with $langle B_z rangle$ about $+1.5$ kG as compared to $langle B_z rangle sim -0.8$ kG for the primary. HD 156424 is thus the second hot binary with two magnetic stars. We are unable to identify a rotational period for HD 156424A. The magnetospheric H$alpha$ emission appears to originate around HD 156424B. Using H$alpha$, as well as other variable spectral lines, we determine a period of about 0.52 d, making HD 156424B one of the most rapidly rotating magnetic hot stars.
We present a new Y dwarf, WISE J030449.03-270508.3, confirmed from a candidate sample designed to pick out low temperature objects from the WISE database. The new object is typed Y0pec following a visual comparison with spectral standards, and lies at a likely distance of 10-17 pc. Its tangential velocity suggests thin disk membership, but it shows some spectral characteristics that suggest it may be metal-poor and/or older than previously identified Y0 dwarfs. Based on trends seen for warmer late type T dwarfs, the Y-band flux peak morphology is indicative of sub-solar metallicity, and the enhanced red wing of the J-band flux peak offers evidence for high gravity and/or low metallicity (with associated model trends suggesting an age closer to ~10 Gyr and mass in the range 0.02-0.03 Mo). This object may thus be extending the population parameter-space of the known Y0 dwarfs.
The spectrum of stars in the submillimeter to centimeter wavelength range remains poorly constrained due to a lack of data for most spectral types. An accurate characterization of stellar emission in this regime is needed to test stellar atmosphere models, and is also essential for revealing emission associated with unresolved circumstellar debris. We present ALMA observations of the three nearby, main-sequence, debris-poor, F-type stars $gamma$ Lep, $gamma$ Vir A, and $gamma$ Vir B at 0.87 and 1.29 millimeters. We use these data to constrain semi-empirical atmospheric models. We discuss the atmospheric structure of these stars, explore potential short term variability, and the potential impact on debris disk studies. These results are part of an ongoing campaign to obtain long wavelength observations of debris-poor stars, entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths (MESAS).
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