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Register a new userFUSE spectroscopy of sdOB primary of the post common-envelope binary LB 3459 (AA Dor)
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Authors
Johannes Fleig
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LB 3459 (AA Dor) is an eclipsing, close, post common-envelope binary consisting of an sdOB primary star and an unseen secondary with an extraordinarly low mass - formally a brown dwarf. A recent NLTE spectral analysis shows a discrepancy with the surface gravity, which is derived from analyses of radial-velocity and lightcurves. We aim at precisely determing of the photospheric parameters of the primary, especially of the surface gravity, and searching for weak metal lines in the far UV. We performed a detailed spectral analysis of the far-UV spectrum of LB 3459 obtained with FUSE by means of state-of-the-art NLTE model-atmosphere techniques. A strong contamination of the far-UV spectrum of LB 3459 by interstellar line absorption hampers a precise determination of the photospheric properties of its primary star. Its effective temperature (42 kK) was confirmed by the evaluation of new ionization equilibria. For the first time, phosphorus and sulfur have been identified in the spectrum of LB 3459. Their photospheric abundances are solar and 0.01 times solar, respectively. From the C III 1174-1177A multiplet, we can measure the rotational velocity of 35 +/- 5 km/sec of the primary of LB 3459 and confirm that the rotation is bound. From a re-analysis of optical and UV spectra, we determine a higher log g = 5.3 (cgs) that reduces the discrepancy in mass determination in comparison to analyses of radial-velocity and lightcurves. However, the problem is not completely solved.
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AA Dor (LB 3459) is an eclipsing, close, single-lined, post common-envelope binary (PCEB) consisting of an sdOB primary star and an unseen secondary with an extraordinary small mass - formally a brown dwarf. The brown dwarf may have been a former planet which survived a common envelope phase and has even gained mass. A recent determination of the components masses from results of state-of-the-art NLTE spectral analysis and subsequent comparison to evolutionary tracks shows a discrepancy between masses derived from radial-velocity and the eclipse curves. Phase-resolved high-resolution and high-SN spectroscopy was carried out with FUSE in order to investigate on this problem. We present preliminary results of an ongoing NLTE spectral analysis of FUSE spectra of the primary.
AA Dor is an eclipsing, close, post common-envelope binary (PCEB). We present a detailed spectral analysis of its sdOB primary star based on observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Due to a strong contamination by interstellar absorption, we had to model both, the stellar spectrum as well as the interstellar line absorption in order to reproduce the FUV observation well and to determine the photospheric parameters precisely.
AA Dor is a close, totally eclipsing, post common-envelope binary with an sdOB-type primary and an extremely low-mass secondary, located close to the mass limit of stable central hydrogen burning. Within error limits, it may either be a brown dwarf or a late M-type dwarf. We aim to extract the secondarys contribution to the phase-dependent composite spectra. The spectrum and identified lines of the secondary decide on its nature. In January 2014, we measured the phase-dependent spectrum of AA Dor with XSHOOTER over one complete orbital period. Since the secondarys rotation is presumable synchronized with the orbital period, its surface strictly divides into a day and night side. Therefore, we may obtain the spectrum of its cool side during its transit and of its hot, irradiated side close to its occultation. We developed the Virtual Observatory (VO) tool TLISA to search for weak lines of a faint companion in a binary system. We identified 53 spectral lines of the secondary in the ultraviolet-blue, visual, and near-infrared XSHOOTER spectra that are strongest close to its occultation. We identified 57 (20 additional) lines in available UVES (Ultraviolet and Visual Echelle Spectrograph) spectra from 2001. The lines are mostly from C II-III and O II, typical for a low-mass star that is irradiated and heated by the primary. We verified the orbital period of P = 22597.033201 +/- 0.00007 s and determined the orbital velocity Ksec = 232.9 (+16.6 / -6.5) km/s of the secondary. The mass of the secondary is Msec = 0.081 (+0.018 / -0.010) Msun and, hence, it is not possible to reliably determine a brown dwarf or an M-type dwarf nature. Although we identified many emission lines of the secondarys irradiated surface, the resolution and signal-to-noise ratio of our UVES and XSHOOTER spectra are not good enough to extract a good spectrum of the secondarys nonirradiated hemisphere.
We present high speed photometry and high resolution spectroscopy of the eclipsing post common envelope binary QS Virginis (QS Vir). Our UVES spectra span multiple orbits over more than a year and reveal the presence of several large prominences passing in front of both the M star and its white dwarf companion, allowing us to triangulate their positions. Despite showing small variations on a timescale of days, they persist for more than a year and may last decades. One large prominence extends almost three stellar radii from the M star. Roche tomography reveals that the M star is heavily spotted and that these spots are long-lived and in relatively fixed locations, preferentially found on the hemisphere facing the white dwarf. We also determine precise binary and physical parameters for the system. We find that the 14,220 +/- 350K white dwarf is relatively massive, 0.782 +/- 0.013Ms, and has a radius of 0.01068 +/- 0.00007Rs, consistent with evolutionary models. The tidally distorted M star has a mass of 0.382 +/- 0.006Ms and a radius of 0.381 +/- 0.003Rs, also consistent with evolutionary models. We find that the magnesium absorption line from the white dwarf is broader than expected. This could be due to rotation (implying a spin period of only ~700 seconds), or due to a weak (~100kG) magnetic field, we favour the latter interpretation. Since the M stars radius is still within its Roche lobe and there is no evidence that its over-inflated we conclude that QS Vir is most likely a pre-cataclysmic binary just about to become semi-detached.
Context. An important ingredient in binary evolution is the common-envelope (CE) phase. Although this phase is believed to be responsible for the formation of many close binaries, the process is not well understood. Aims. We investigate the characteristics of the population of post-common-envelope binaries (PCEB). As the evolution of these binaries and their stellar components are relatively simple, this population can be directly used to constraint CE evolution. Methods. We use the binary population synthesis code SeBa to simulate the current-day population of PCEBs in the Galaxy. We incorporate the selection effects in our model that are inherent to the general PCEB population and that are specific to the SDSS survey, which enables a direct comparison for the first time between the synthetic and observed population of visible PCEBs. Results. We find that selection effects do not play a significant role on the period distribution of visible PCEBs. To explain the observed dearth of long-period systems, the {alpha}-CE efficiency of the main evolutionary channel must be low. In the main channel, the CE is initiated by a red giant as it fills its Roche lobe in a dynamically unstable way. Other evolutionary paths cannot be constrained more. Additionally our model reproduces well the observed space density, the fraction of visible PCEBs amongst white dwarf (WD)- main sequence (MS) binaries, and the WD mass versus MS mass distribution, but overestimates the fraction of PCEBs with helium WD companions.
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