V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary1 (original) (raw)
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New Astronomy, 2007
The results of a long-term UBV photometric monitoring of the red supergiant (RSG) star V424 Lac are presented. V424 Lac shows multiperiodic brightness variations which can be attributed to pulsational oscillations. A much longer period (P = 1601 d), that allows us to classify this star as a long secondary period variable star (LSPV) has been also detected. The B À V and U À B color variations related to the long secondary period (LSP) are similar to those related to the shorter periods, supporting the pulsational nature of LSP. The long period brightness variation of V424 Lac is accompanied by a near-UV (NUV) excess, which was spectroscopically detected in a previous study . ApJ 634, 1286 and which is now found to be variable from photometry. On the basis of the results found for V424 Lac, the NUV excess recently found in a number of RSGs may be due not solely to circumstellar dust but may also have a contribution from a still undetected LSP variability.
Simultaneous optical and near-IR photometry of 4U1957+115 - a missing secondary star
Monthly Notices of the Royal Astronomical Society, 2014
We report the results of quasi-simultaneous optical and NIR photometry of the lowmass X-ray binary, 4U 1957+115. Our observations cover B, V, R, I, J, H and K-bands and additional time-series NIR photometry. We measure a spectral energy distribution, which can be modelled using a standard multi-temperature accretion disc, where the disc temperature and radius follow a power-law relation. Standard accretion disc theory predicts the power law exponent to be -3/4, and this yields, perhaps surprisingly, acceptable fits to our SED. Given that the source is a persistent X-ray source, it is however likely that the accretion disc temperature distribution is produced by X-ray heating, regardless of its radial dependence. Furthermore, we find no evidence for any emission from the secondary star at any wavelength. However, adding a secondary component to our model allows us to derive a 99% lower limit of 14 or 15 kpc based on Monte Carlo simulations and using either an evolved K2 or G2V secondary star respectively. In >60% of cases the distance is >80kpc. Such large distances favor models with a massive (>15 M ⊙ ) black hole primary. Our quasi-simultaneous J and V-band time-series photometry, together with the SED, reveals that the optical/NIR emission must originate in the same region i.e. the accretion disc. The likely extreme mass ratio supports suggestions that the accretion disc must be precessing which, depending on the length of the precession period, could play a major part in explaining the variety of optical light curve shapes obtained over the last two decades.
HE 0017+0055: A probable pulsating CEMP-rs star and long-period binary
Astronomy & Astrophysics, 2015
Context. A large fraction of the carbon-enhanced, extremely metal-poor halo giants ([Fe/H] < −2.5) are also strongly enriched in neutron-capture elements from the s process (CEMP-s stars). The conventional explanation for the properties of these stars is mass transfer from a nearby binary companion on the asymptotic giant branch (AGB). This scenario leads to a number of testable predictions in terms of the properties of the putative binary system and the resulting abundance pattern. Among the CEMP stars, some stars further exhibit overabundances in r-process elements on top of the s-process enrichment, and are tagged CEMP-rs stars. Although the nucleosynthesis process responsible for this kind of mixed abundance pattern is still under debate, CEMP-rs stars seem to belong to binary systems as do CEMP-s stars. Aims. Our aim is to present and analyse in detail our comprehensive data set of systematic radial-velocity measurements and highresolution spectroscopy of the CEMP star HE 0017+0055. Methods. Our precise radial-velocity monitoring of HE 0017+0055 over 2940 days (8 yr) with the Nordic Optical Telescope and Mercator telescopes exhibits variability, with a period of 384 d and amplitude of 540 ± 27 m s −1 superimposed on a nearly linear long-term decline of ∼1 m s −1 day −1. We used high-resolution HERMES/Mercator and Keck/HIRES spectra to derive elemental abundances with 1D LTE MARCS models. A metallicity of [Fe/H] ∼ −2.4 is found, along with s-process overabundances of the order of 2 dex (with the exception of [Y/Fe] ∼ +0.5), and most notably overabundances of r-process elements like Sm, Eu, Dy, and Er in the range 0.9−2.0 dex. With [Ba/Fe] > 1.9 dex and [Eu/Fe] = 2.3 dex, HE 0017+0055 is a CEMP-rs star. We used the derived atmospheric parameters and abundances to infer HE 0017+0055 evolutionary status from a comparison with evolutionary tracks. Results. HE 0017+0055 appears to be a giant star below the tip of the red giant branch. The s-process pollution must therefore originate from mass transfer from a companion formerly on the AGB, which is now a carbon-oxygen white dwarf (WD). If the 384 d velocity variations are attributed to the WD companion, its orbit must be seen almost face-on, with i ∼ 2.3 • , because the mass function is very small: f (M 1 , M 2) = (6.1 ± 1.1) × 10 −6 M. Alternatively, the WD orbital motion could be responsible for the long-term velocity variations, with a period of several decades. The 384 d variations should then be attributed either to a low-mass inner companion (perhaps a brown dwarf, depending on the orbital inclination), or to stellar pulsations. The latter possibility is made likely by the fact that similar low-amplitude velocity variations, with periods close to 1 yr, have been reported for other CEMP stars in a companion paper. A definite conclusion about the origin of the 384 d velocity variations should however await the detection of synchronous low-amplitude photometric variations.
Discovery of a cataclysmic variable with a sub-stellar companion
Astronomy & Astrophysics, 2001
We find that the ROSAT source 1RXS J105010.3-140431 is a cataclysmic variable with orbital period of 88.6 minutes and a spectrum closely resembling WZ Sge. In particular, emission lines are flanked by Stark-broadened absorption wings probably originating in the photosphere of a compact object. The Balmer absorption lines can be modeled by the spectrum of a DA white dwarf with 13 000 <Teff<< T_{eff} <<Teff< 24 000 K. The strong absorption lines allowed us to obtain direct radial velocities of the white dwarf using the cross-correlation technique. We find an extremely low white dwarf radial velocity half amplitude, KwdK_{wd}Kwd = 4 pm\pmpm 1 km s$^{-1}$. This is consistent with the upper limit obtained from the H$\alpha$ emission line wing K < 20 km s$^{-1}$. The corresponding mass function is incompatible with a main sequence secondary, but is compatible with a post orbital period minimum cataclysmic variable with a brown dwarf-like secondary. The formal solution gives a secondary mass of 10-20 jovian masses. Doppler maps for the emission lines and the hypothesis of black-body emission indicate a steady state (T simr−3/4\sim r^{-3/4}simr−3/4) accretion disk mainly emitting in H$\alpha$ and an optically thicker hotspot with a strong contribution to the higher order Balmer lines and \ion{He}{I} 5875. As in other long cycle length dwarf novae, evidence for inner disk removal is found from the analysis of the emission lines.
GSC 4560–02157: a new long-period eclipsing cataclysmic variable star
Research in Astronomy and Astrophysics, 2015
We study the newly discovered variable star GSC 4560-02157. CCD photometry was performed in 2013-2014, and a spectrum was obtained with the 6-m telescope in June, 2014. GSC 4560-02157 is demonstrated to be a short-period (P = 0.265359 d) eclipsing variable star. All its flat-bottom primary minima are approximately at the same brightness level, while the star's out-of-eclipse brightness and brightness at secondary minimum varies considerably (by up to 0.6 m) from cycle to cycle. Besides, there are short-term (time scale of 0.03-0.04 days) small-amplitude brightness variations out of eclipse. This behavior suggests cataclysmic nature of the star, confirmed with a spectrum taken on June 5, 2014. The spectrum shows numerous emissions of the hydrogen Balmer series, HeI, HeII.
Two Long-period Cataclysmic Variable Stars: ASASSN-14ho and V1062 Cyg
We report spectroscopy and photometry of the cataclysmic variable stars ASASSN-14ho and V1062 Cyg. Both are dwarf novae with spectra dominated by their secondary stars, which we classify approximately as K4 and M0.5, respectively. Their orbital periods, determined mostly from the secondary stars' radial velocities, proved to be nearly identical, respectively 350.14 ± 0.15 and 348.25 ± 0.60 min. The Hα emission line in V1062 Cyg displays a relatively sharp emission component that tracks the secondary's motion, which may arise on the irradiated face of the secondary; this is not often seen and may indicate an unusually strong flux of ionizing radiation. Both systems exhibit double-peaked orbital modulation consistent with ellipsoidal variation from the changing aspect of the secondary. We model these variations to constrain the orbital inclination i, and estimate approximate component masses based on i and the secondary velocity amplitude K 2 .
Monthly Notices of the Royal Astronomical Society, 2020
We report the discovery of a relatively bright eclipsing binary system, which consists of a white dwarf (WD) and a main-sequence K7 star with clear signs of chromospheric and spot activity. The light curve of this system shows ∼0.2 mag ellipsoidal variability with a period of 0.297549 d and a short total eclipse of the WD. Based on our analysis of the spectral and photometric data, we estimated the parameters of the system. The K7V star is tidally deformed but does not fill its Roche lobe (the filling factor is about 0.86). The orbital inclination is i = 73.circ1pm0.circ273{_{.}^{\circ}}1 \pm 0{_{.}^{\circ}}273.circ1pm0.circ2, and the mass ratio is q = M2/M1 ≈ 0.88. The parameters of the K7V star are M2 ≈ 0.64 M⊙, R2 = 0.645 ± 0.012R⊙, and T2 ≈ 4070 K. The parameters of the WD are M1 ≈ 0.72 M⊙, R1 = 0.013 ± 0.003R⊙, and T1 = 8700 ± 1100 K. Photometric observations in different bands revealed that the maximum depth of the eclipse is in the SDSS r filter, which is unusual for a system of a WD and a late main-sequenc...
RX J0513.1+0851 and RX J0539.9+0956: Two Young, Rapidly Rotating Spectroscopic Binary Stars
The Astronomical Journal, 2013
RX J0513.1+0851 and RX J0539.9+0956 were previously identified as young, low-mass, single-lined spectroscopic binary systems and classified as weak-lined T Tauri stars at visible wavelengths. Here we present radial velocities, spectral types, v sin i values, and flux ratios for the components in these systems resulting from two-dimensional cross-correlation analysis. These results are based on highresolution, near-infrared spectroscopy taken with the Keck II telescope to provide a first characterization of these systems as double-lined rather than single-lined. It applies the power of infrared spectroscopy to the detection of cool secondaries; the flux scales as a less steep function of mass in the infrared than in the visible, thus enabling an identification of low-mass secondaries. We found that the RX J0513.1+0851 and RX J0539.9+0956 primary stars are fast rotators, 60 km s −1 and 80 km s −1 respectively; this introduces extra difficulty in the detection of the secondary component as a result of the quite broad absorption lines. To date, these are the highest rotational velocities measured for a pre-main sequence spectroscopic binary. The orbital parameters and mass ratios were determined by combining new visible light spectroscopy with our infrared data for both systems. For RX J0513.1+0851, we derived a period of ∼4 days and a mass ratio of q = 0.46 ± 0.01 and for RX J0539.9+0956, a period of ∼1117 days and a mass ratio of q = 0.66 ± 0.01. Based on our derived properties for the stellar components, we estimate the luminosities and hence distances to these binaries at 220 pc and 90 pc. They appear to be significantly closer than previously estimated.
Two new accreting, pulsating white dwarfs: SDSS J1457+51 and BW Sculptoris
Monthly Notices of the Royal Astronomical Society, 2012
We report the discovery of rapid periodic signals in the light curves of two cataclysmic variables with prominent white-dwarf components in their spectra, SDSS J1457+51 and BW Sculptoris. These stars therefore appear to be new members of the GW Lib class of variable star, in which the fast periodic (and non-commensurate with the orbital period) signals are believed to arise from non-radial pulsations in the underlying white dwarf. The power spectra of both stars show complex signals with primary periods near 10 and 20 minutes. These signals change in frequency by a few percent on a timescale of weeks or less, and probably contain an internal fine structure unresolved by our observations. We also detect double-humped waves signifying the underlying orbital periods, near 78 minutes for both stars.
The Astrophysical Journal, 2006
We present spectroscopic and photometric observations of the eclipsing system V1061 Cyg, previously thought to be a member of the rare class of "cool Algols". We show that it is instead a hierarchical triple system in which the inner eclipsing pair (with P = 2.35 days) is composed of main-sequence stars and is well detached, and the third star is also visible in the spectrum. We combine the radial velocities for the three stars, times of eclipse, and intermediate astrometric data from the HIPPARCOS mission (abscissae residuals) to establish the elements of the outer orbit, which is eccentric and has a period of 15.8 yr. We determine accurate values for the masses, radii, and effective temperatures of the binary components: M Aa = 1.282 ± 0.015 M ⊙ , R Aa = 1.615 ± 0.017 R ⊙ , and T Aa eff = 6180 ± 100 K for the primary (star Aa), and M Ab = 0.9315 ± 0.0068 M ⊙ , R Ab = 0.974 ± 0.020 R ⊙ , and T Ab eff = 5300 ± 150 K for the secondary (Ab). The masses and radii have relative errors of only 1-2%. Both stars are rotating rapidly (v sin i values are 36±2 km s −1 and 20±3 km s −1 ) and have their rotation synchronized with the orbital motion. There are signs of activity including strong X-ray emission and possibly spots. The mass of the tertiary is determined to be M B = 0.925 ± 0.036 M ⊙ and its effective temperature is T B eff = 5670 ± 150 K.