Search

We present follow-up photometry and spectroscopy of the rapidly pulsating subdwarf B star EC 22221-3152. Using the SAAO 1.0-m telescope and the 0.4-m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) at the Cerro Tololo Inter-American Observatory (CTIO), we monitored the star photometrically for one week. By combining data from both telescopes, we were able to resolve 18 significant periodicities in the light curve. Seven of these signals consist of combination frequencies, a first harmonic, and possible rotational splittings that would be indicative of an 8.2-d rotation period. The remaining 11 periodicities appear to represent independent oscillation modes, including three not originally detected in the discovery work. Time series spectroscopy obtained with the Goodman spectrograph on the 4.1-m SOAR telescope reveals possible velocity variations corresponding to two of the observed pulsation modes. From atmospheric model fits to the spectra, we derive K, log g = 5.86 ± 0.15, and log N(He)/N(H) = −1.4 ± 0.3 and confirm the star’s status as one of the hottest sdBVr stars currently known. [ABSTRACT FROM AUTHOR]

We report the results of high-resolution (R ∼ 80,000) spectroscopic observations of the emission-line object HD 85567, which has been classified as an FS CMa type object or a pre-main-sequence star. The main goal is to put more constraints on the object’s fundamental parameters, as well as on its nature and evolutionary state. Absorption lines in the spectrum of HD 85567 were found to be similar to those of mid-B-type dwarfs and correspond to the following fundamental parameters: Teff = 15,000 ± 500 K, km s−1, and . The interstellar extinction, AV = 0.50 ± 0.02 mag, was measured using the strengths of some diffuse interstellar bands. We also obtained UBV(RI)c images of a 10′ × 10′ region around the object. Photometry of projectionally close stars was used to derive an interstellar extinction law in this direction and resulted in a distance of 1300 ± 100 pc to the object and a luminosity of log L/L⊙ = 3.3 ± 0.2. We found no significant radial velocity variations of the absorption lines in the spectra of HD 85567 obtained during two-month-long periods of time in 2012 and 2015. Our analysis of the spectroscopic and photometric data available for the star led us to a conclusion that it cannot be a pre-main-sequence Herbig Ae/Be star. We argue that the circumstellar gas and dust were produced during the object’s evolution as most likely a binary system, which contains an undetected secondary component and is unlikely to be a merger product. [ABSTRACT FROM AUTHOR]

We studied two objects identified as cataclysmic variables (CVs) with periods exceeding the natural boundary for Roche-lobe-filling zero-age main sequence (ZAMS) secondary stars. We present observational results for V1082 Sgr with a 20.82 hr orbital period, an object that shows a low luminosity state when its flux is totally dominated by a chromospherically active K star with no signs of ongoing accretion. Frequent accretion shutoffs, together with characteristics of emission lines in a high state, indicate that this binary system is probably detached, and the accretion of matter on the magnetic white dwarf takes place through stellar wind from the active donor star via coupled magnetic fields. Its observational characteristics are surprisingly similar to V479 And, a 14.5 hr binary system. They both have early K-type stars as donor stars. We argue that, similar to the shorter-period prepolars containing M dwarfs, these are detached binaries with strong magnetic components. Their magnetic fields are coupled, allowing enhanced stellar wind from the K star to be captured and channeled through the bottleneck connecting the two stars onto the white dwarf’s magnetic pole, mimicking a magnetic CV. Hence, they become interactive binaries before they reach contact. This will help to explain an unexpected lack of systems possessing white dwarfs with strong magnetic fields among detached white+red dwarf systems. [ABSTRACT FROM AUTHOR]