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Register a new userAn Halpha-selected sample of cataclysmic variables -- I. Observations of newly discovered systems
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Added by
Magaretha Pretorius
Publication date
2008
fields
Physics
and research's language is
English
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Strong selection effects are present in observational samples of cataclysmic variables (CVs), complicating comparisons to theoretical predictions. The selection criteria used to define most CV samples discriminate heavily against the discovery of short-period, intrinsically faint systems. The situation can be improved by selecting CVs for the presence of emission lines. For this reason, we have constructed a homogeneous sample of CVs selected on the basis of Halpha emission. We present discovery observations of the 14 CVs and 2 additional CV candidates found in this search. The orbital periods of 11 of the new CVs were measured; all are above 3 h. There are two eclipsing systems in the sample, and one in which we observed a quasi-periodic modulation on a sim 1000 s time-scale. We also detect the secondary star in the spectrum of one system, and measure its spectral type. Several of the new CVs have the spectroscopic appearance of nova-like variables (NLs), and a few display what may be SW Sex star behaviour. In a companion paper, we discuss the implications of this new sample for CV evolution.
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We present time-resolved photometry of five relatively poorly-studied cataclysmic variables: V1193 Ori, LQ Peg, LD 317, V795 Her, and MCT 2347-3144. The observations were made using four 1m-class telescopes for a total of more than 250 h of observation and almost 16,000 data points. For LQ Peg WHT spectroscopic data have been analysed as well. The light curves show a wide range of variability on different time scales from minutes to months. We detect for the first time a brightness variation of 0.05 mag in amplitude in V1193 Ori on the same timescale as the orbital period, which we interpret as the result of the irradiation of the secondary. A 20-min quasi-periodic oscillation is also detected. The mean brightness of the system has changed by 0.5 mag on a three-month interval, while the flickering was halved. In LQ Peg a 0.05 mag modulation was revealed with a period of about 3 h. The flickering was much smaller, of the order of 0.025 mag. A possible quasi-periodic oscillation could exist near 30 min. For this object, the WHT spectra are single-peaked and do not show any radial-velocity variations. The data of LD 317 show a decrease in the mean magnitude of the system. No periodic signal was detected but this is certainly attributable to the very large flickering observed: between 0.07 and 0.1 mag. For V795 Her, the 2.8-hour modulation, thought to be a superhump arising from the precession of the disc, is present. We show that this modulation is not stable in terms of periodicity, amplitude, and phase. Finally, for MCT 2347-3144, a clear modulation is seen in a first dataset obtained in October 2002. This modulation is absent in August 2003, when the system was brighter and showed much more flickering.
We report on the properties of 71 known cataclysmic variables (CVs) in photometric Halpha emission line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Halpha Survey of the northern galactic plane (IPHAS) will soon provide r, i and narrow-band Halpha measurements down to r simeq 20 for all northern objects between -5 degrees < b < +5 degrees. IPHAS thus provides a unique resource, both for studying the emission line properties of known CVs and for constructing a new CV sample selected solely on the basis of Halpha excess. Our goal here is to carry out the first task and prepare the way for the second. In order to achieve this, we analyze data on 19 CVs already contained in the IPHAS data base and supplement this with identical observations of 52 CVs outside the galactic plane. Our key results are as follows: (i) the recovery rate of known CVs as Halpha emitters in a survey like IPHAS is simeq 70 per cent; (ii) of the simeq 30 per cent of CVs which were not recovered simeq 75 per cent were clearly detected but did not exhibit a significant Halpha excess at the time of our observations; (iii) the recovery rate depends only weakly on CV type; (iv) the recovery rate depends only weakly on orbital period; (v) short-period dwarf novae tend to have the strongest Halpha lines. These results imply that photometric emission line searches provide an efficient way of constructing CV samples that are not biased against detection of intrinsically faint, short-period systems.
We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telescope (INT) Photometric H alpha Survey of the northern Galactic plane (IPHAS). Three of the systems have been the subject of further follow-up observations. For the CV candidates IPHAS J013031.90+622132.4 and IPHAS J051814.34+294113.2, time-resolved optical spectroscopy has been obtained and radial-velocity measurements of the H alpha emission-line have been used to estimate their orbital periods. A third CV candidate (IPHAS J062746.41+ 014811.3) was observed photometrically and found to be eclipsing. All three systems have orbital periods above the CV period-gap of 2-3 h. We also highlight one other system, IPHAS J025827.88+635234.9, whose spectrum distinguishes it as a likely high luminosity object with unusual C and N abundances.
A sample of Cataclysmic Variables (CVs) is presented including spectroscopically identified 380 spectra of 245 objects, of which 58 CV candidates are new discoveries. The BaggingTopPush and the Random Forest algorithms are applied to the Fifth Data Release (DR5) of LAMOST to retrieve CVs with strong emission lines and with broad absorption lines respectively. Based on spectroscopic classification, 134 dwarf novae, 41 nova-like variables and 19 magnetic CVs are identified from the sample. In addition, 89 high--inclination systems and 33 CVs showing companion stars are recognized and discussed for their distinct spectral characteristics. Comparisons between CVs from LAMOST and from published catalogs are made in spatial and magnitude distribution, and the difference of their locus in Gaia color--absolute magnitude diagram (CaMD) are also investigated. More interestingly, for two dwarf novae observed through LAMOST and SDSS in different epoch, their spectra both in quiescence phase and during outburst are exhibited.
The RApid Temporal Survey (RATS) is a survey to detect objects whose optical intensity varies on timescales of less than ~70 min. In our pilot dataset taken with the INT and the Wide Field Camera in Nov 2003 we discovered nearly 50 new variable objects. Many of these varied on timescales much longer than 1 hr. However, only 4 objects showed a modulation on a timescale of 1 hour or less. This paper presents followup optical photometry and spectroscopy of these 4 objects. We find that RAT J0455+1305 is a pulsating (on a period of 374 sec) subdwarf B (sdB) star of the EC 14026 type. We have modelled its spectrum and determine Teff = 29,200+/- 1900K and log g = 5.2+/-0.3 which locates it on the cool edge of the EC 14026 instability strip. It has a modulation amplitude which is one of the highest of any known EC 14026 star. Based on their spectra, photometric variability and their infra-red colours, we find that RAT J0449+1756, RAT J0455+1254 and RAT J0807+1510 are likely to be SX Phe stars - dwarf Delta Sct stars. Our results show that our observing strategy is a good method for finding rare pulsating stars.
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