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Register a new userCXOGBSJ174444.7-260330: a new long orbital period cataclysmic variable in a low state
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We present phase-resolved spectroscopy and photometry of a source discovered with the Chandra Galactic Bulge Survey (GBS), CXOGBSJ174444.7-260330 (aka CX93 and CX153 in the previously published GBS list). We find two possible values for the orbital period P, differing from each other by 13 seconds. The most likely solution is P =5.69014(6) hours. The optical lightcurves show ellipsoidal modulations, whose modeling provides an inclination of 32+-1 degrees for the most likely P. The spectra are dominated by a K5V companion star (the disc veiling is <~5%). Broad and structured emission from the Balmer lines is also detected, as well as fainter emission from HeI. From the absorption lines we measure K2 =117+-8km/s and v sin i = 69+-7km/s. By solving the system mass function we find M1=0.8+-0.2Msun for the favored P and i, consistent with a white dwarf accretor, and M2=0.6+-0.2Msun. We estimate a distance in the range 400-700 pc. Although in a low accretion state, both spectroscopy and photometry provide evidence of variability on a timescale of months or faster. Besides finding a new, long orbital period cataclysmic variable in a low accretion state, this work shows that the design of the GBS works efficiently to find accreting X-ray binaries in quiescence, highlighting that the spectra of CVs in a low-accretion state can at times appear suggestive of a quiescent neutron star or a black hole system.
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We present modeling of the long-term optical light curve and radial velocity curve of the binary stellar system CXOGBS J175553.2-281633, first detected in X-rays in the textit{Chandra} Galactic Bulge Survey. We analyzed 7 years of optical I-band photometry from OGLE and found long-term variations from year to year. These long-term variations can most likely be explained with by either variations in the luminosity of the accretion disk or a spotted secondary star. The phased light curve has a sinusoidal shape, which we interpret as being due to ellipsoidal modulations. We improve the orbital period to be $P = 10.34488 pm 0.00006$ h with a time of inferior conjunction of the secondary star $T_0 = {rm HJD } 2455260.8204 pm 0.0008$. Moreover, we collected 37 spectra over 6 non-consecutive nights. The spectra show evidence for an evolved K7 secondary donor star, from which we obtain a semi-amplitude for the radial velocity curve of $K_2 = 161 pm 6 $ km s$^{-1}$. Using the light curve synthesis code {tt XRbinary}, we derive the most likely orbital inclination for the binary of $i = 63.0pm0.7$ deg, a primary mass of $M_1 = 0.83 pm 0.06$ M$_odot$, consistent with a white dwarf accretor, and a secondary donor mass of $M_2 = 0.65 pm 0.07$ M$_odot$, consistent with the spectral classification. Therefore, we identify the source as a long orbital period cataclysmic variable star.
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