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تسجيل مستخدم جديدExploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects
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A. S. Oliveira
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The increasing number of synoptic surveys made by small robotic telescopes, such as the photometric Catalina Real-Time Transient Survey (CRTS), represents a unique opportunity for the discovery of variable sources and improves the statistical samples of such classes of objects. Our goal is the discovery of magnetic Cataclysmic Variables (mCVs). These are rare objects, which probe interesting accretion scenarios controlled by the white dwarf magnetic field. In particular, improved statistics of mCVs would help to address open questions on their formation and evolution. We performed an optical spectroscopy survey to search for signatures of magnetic accretion in 45 variable objects selected mostly from the CRTS. In this sample we found 32 CVs, 22 being mCV candidates from which 13 are previously unreported as such. If the proposed classifications are confirmed, it would represent an increase of 4% in the number of known polars and 12% in the number of known IPs. A fraction of our initial sample was classified as extragalactic sources or other types of variable stars by the inspection of the identification spectra. Despite the inherent complexity in identifying a source as a mCV, variability-based selection followed by spectroscopic snapshot observations has proved to be an efficient strategy for their discoveries, being a relatively inexpensive approach in terms of telescope time.
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This is the second paper of a series presenting our search for magnetic Cataclysmic Variables (mCVs) among candidates selected mostly from the Catalina Real-Time Transient Survey (CRTS). We present the identification spectra, obtained at the SOAR Tel
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>30^circ$), and detected 6 intermediate polars (IPs) and 24 polars. If we assume that the 30 mCVs included in the RBS are representative of the intrinsic population, the space density of mCVs is $8^{+4}_{-2} times 10^{-7},{rmpc^{-3}}$. Considering polars and IPs separately, we find $rho_{polar}=5^{+3}_{-2} times 10^{-7},{rm pc^{-3}}$ and $rho_{IP}=3^{+2}_{-1} times 10^{-7},{rm pc^{-3}}$. Allowing for a 50% high-state duty cycle for polars (and assuming that these systems are below the RBS detection limit during their low states) doubles our estimate of $rho_{polar}$ and brings the total space density of mCVs to $1.3^{+0.6}_{-0.4} times 10^{-6},{rm pc^{-3}}$. We also place upper limits on the sizes of faint (but persistent) mCV populations that might have escaped detection in the RBS. Although the large uncertainties in the $rho$ estimates prevent us from drawing strong conclusions, we discuss the implications of our results for the evolutionary relationship between IPs and polars, the fraction of CVs with strongly magnetic white dwarfs (WDs), and for the contribution of mCVs to Galactic populations of hard X-ray sources at $L_X ga 10^{31} {rm erg/s}$. Our space density estimates are consistent with the very simple model where long-period IPs evolve into polars and account for the whole short-period polar population. We find that the fraction of WDs that are strongly magnetic is not significantly higher for CV primaries than for isolated WDs. Finally, the space density of IPs is sufficiently high to explain the bright, hard X-ray source population in the Galactic Centre.
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