We use an independent new sample of cataclysmic variables (CVs), constructed by selecting objects for Halpha emission, to constrain the properties of the intrinsic CV population. This sample is restricted to systems that are likely to be non-magnetic and unevolved; it consists of 17 CVs, of which at least 10 have orbital periods above 3 h. We find that even very generous allowance for selection effects is not sufficient to reconcile the large ratio of short- to long-period CVs predicted by standard CV evolution theory with the observed sample, possibly implying that short-period systems evolve faster than predicted by the disrupted magnetic braking model. This would require that an angular momentum loss mechanism, besides gravitational radiation, acts on CVs with orbital periods below the period gap. To bring the model into agreement with observations, the rate of angular momentum loss below the period gap must be increased by a factor of at least 3, unless the model also over estimates the angular momentum loss rate of long-period CVs.
We present results from our phase-resolved spectroscopy of the newly identified cataclysmic variable Halpha0242-2802. Halpha0242-2802 was identified from a deep UK Schmidt Halpha-R band survey as a candidate cataclysmic variable. Although initial spectroscopy revealed an optical spectrum very similar to that of the famous short orbital period system WZ Sge, the analysis of our data shows that this is not the case. Halpha0242-28 differs from WZ Sge in both the accretion disk structure and the orbital period. In particular, Halpha0242-28 appears to be a system which has not reached the orbital p…
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…
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 ca…
We present a spectroscopic study of the long-recurrence-time dwarf nova V592 Herculis based on observations obtained during its August 1998 superoutburst. From the analysis of the radial velocities of the Halpha emission line we find a most likely orbital period of 85.5 +- 0.4 minutes, but the 91.2 +- 0.6 minutes alias cannot be completely discarded. Both periods imply a very small period excess and supports the brown-dwarf like nature of the secondary star.
A deep (R ~ 19.5) photographic Halpha Survey of the southern Galactic Plane was recently completed using the UK Schmidt Telescope at the AAO. In addition, we have recently started a similar, CCD-based survey of the northern Galactic Plane using the Wide Field Camera on the INT. Both surveys aim to provide information on many types of emission line objects, such as planetary nebulae, luminous blue variables and interacting binaries. Here, we focus specifically on the ability of Halpha emission line surveys to discover cataclysmic variables (CVs). Follow-up observations have already begun, and w…
We study the luminosity function and clustering properties of subsamples of local galaxies selected from the Stromlo-APM survey by the rest-frame equivalent width (EW) of the Halpha emission line. The b_J luminosity function of star-forming galaxies has a significantly steeper faint-end slope than that for quiescent galaxies: the majority of sub-L* galaxies are currently undergoing significant star formation. Emission line galaxies are less strongly clustered, both amongst themselves, and with the general galaxy population, than quiescent galaxies. Thus as well as being less luminous, star-for…
We present time-series photometry of nine cataclysmic variables: EI UMa, V844Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.12, V1315 Aql and LN UMa. The observations were conducted at various observatories, covering 170 hours and comprising 7,850 data points in total. For the majority of targets we confirm previously reported periodicities and for some of them we give, for the first time, their spectroscopic orbital periods. For those dwarf-nova systems which we observed during both quiescence and outburst, the increase in brightness was followed by a decrease in the am…
We provide the first minimum light spectroscopic observations for 21 previously known or suspected faint cataclysmic variable candidates. The sources were selected from the Downes et al. (2001) living edition catalog and the identified candidates have minimum light magnitudes of V~18-22. We confirm 15 of the candidates to be cataclysmic variables.
We use narrowband imaging (FWHM = 70 A) to select a sample of emission line galaxies between 0.20 <~ z <~ 1.22 in two fields covering 0.5 sq. deg. We use spectroscopic follow-up to select a sub-sample of Halpha emitting galaxies at z ~ 0.24 and determine the Halpha luminosity function and star formation density at z ~ 0.24 for both of our fields. Corrections are made for imaging and spectroscopic incompleteness, extinction and interloper contamination on the basis of the spectroscopic data. When compared to each other, we find the field samples differ by Δα= 0.2 in faint end slope and Δ\log [ …
We present VLT and Magellan spectroscopy and NTT photometry of nine faint cataclysmic variables (CVs) which were spectroscopically identified by the SDSS. We measure orbital periods for five of these from the velocity variations of the cores and wings of their Halpha emission lines. Four of the five have orbital periods shorter than the 2-3 hour period gap observed in the known population of CVs. SDSS J004335.14-003729.8 has an orbital period of Porb = 82.325 +/- 0.088 min; Doppler maps show emission from the accretion disc, bright spot and the irradiated inner face of the secondary star. In i…
We have identified the 1.4 GHz radio source FIRST J102347.6+003841 (hereafter FIRST J1023+0038) with a previously unknown 17th-mag Galactic cataclysmic variable (CV). The optical spectrum resembles that of a magnetic (AM Herculis- or DQ Herculis-type) CV. Five nights of optical CCD photometry showed variations on timescales of minutes to hours, along with rapid flickering. A re-examination of the FIRST radio survey data reveals that the radio detection was based on a single 6.6 mJy flare; on two other occasions the source was below the ~1 mJy survey limit. Several other magnetic CVs are known …
We report on the discovery of two new faint cataclysmic variables. The objects were selected as candidates from two different imaging surveys aimed at the discovery of such faint systems. One survey used color and variability while the other used color and H$_α$ emission as selection criteria. We present our spectra of the two new variables and discuss their properties. A discussion of the implication of these discoveries on the space density of faint cataclysmic variables is presented.
We present time-series VLT spectroscopy and NTT photometry of the cataclysmic variable SDSS J220553.98+115553.7, which contains a pulsating white dwarf. We determine a spectroscopic orbital period of 82.825 +/- 0.089 min from velocity measurements of the Halpha emission line. A period analysis of the light curves reveals a dominant periodicity at 44.779 +/- 0.038 min which is not related to the spectroscopic period. However, the light curves do not exhibit a variation at any frequency which is attributable to GW Lib type pulsations, to a detection limit of 5 mmag. This non-detection is in cont…
We study the star formation rate and dust extinction properties of a sample of nearby star forming galaxies as derived from Halpha and UV (2000 A) observations and we compare them to those of a sample of starburst galaxies. The dust extinction in Halpha is estimated from the Balmer decrement and the extinction in UV using the FIR to UV flux ratio or the attenuation law for starburst galaxies of Calzetti et al. The Halpha and UV emissions are strongly correlated with a very low scatter for the star forming objects and with a much higher scatter for the starburst galaxies. The Halpha to UV flux …
We investigate the systematic variation of the [OII]3727/Halpha flux line ratio as a function of various galaxy properties, i.e., luminosity, metallicity, reddening, and excitation state, for a sample of 1124 emission-line galaxies, with a mean redshift z ~ 0.06, drawn from the Two Degree Field Galaxy Redshift Survey. The mean observed and extinction-corrected emission-line flux ratios agree well with the values derived from the $B$-band selected Nearby Field Galaxy Survey galaxy sample, but are significantly different from the values obtained from the Halpha-selected Universidad Complutense d…
We report the results of near-infrared VLT-ISAAC spectroscopy of a sample of 12 galaxies at z = 0.4-1.4, drawn from the ISOCAM survey of the Hubble Deep Field South. We find that the rest frame R-band spectra of the ISOCAM galaxies resemble those of powerful dust-enshrouded starbursts. Halpha emission is detected in 11 out of 12 objects down to a flux limit of 7x10^(-17) erg/cm^2/s, corresponding to a luminosity limit of 10^41 erg/s at z = 0.6, (for an Ho = 50 and Omega = 0.3 cosmology). From the Halpha luminosities in these galaxies we derive estimates of the star formation rate in the range …
We present the initial results from a study of the SNR population in a sample of six nearby galaxies (NGC 2403, NGC 4214, NGC 4449, NGC 5204, NGC 3077, NGC 4395) based on Chandra archival data. We discuss the analysis of the Chandra data and we present candidate SNR sources selected on the basis of their X-ray colours. We also present deep [S II] 6716 & 6731 A and Halpha line images for most of the galaxies in our sample, which provide optically selected samples of SNRs. Comparison of the X-ray results with the complementary optical observations provides a more complete picture of the SNR popu…
The [OII]3727 emission line is frequently used as an indicator of the star formation rate (SFR) despite its complex dependence on metallicity and excitation conditions. We have analysed the properties of the [OII] and Halpha emission lines for a complete sample of local Halpha-selected galaxies, the Universidad Complutense de Madrid (UCM) survey. We find a large scatter in the [OII]/Halpha line ratios, although the scatter in the extinction-corrected [OII]^0/Halpha^0 ratio is considerably smaller. We also find that the [OII]/Halpha ratios are reasonably well correlated with the absolute B- and…
We review the properties of the currently known CV population from an accountants point of view. In particular, it is examined to what extent different selection mechanisms (variability, X-ray emission, colours, spectroscopic properties) affect the observed CV orbital period distribution. Large-scale surveys provide homogeneously selected CV samples, for which observational biases can in principle be modelled. Such samples will eventually provide the essential observational input for an improved understanding of CV evolution, and we highlight the impact of several completed and on-going survey…
We present time-resolved spectroscopy and photometry of the bright cataclysmic variable LS Peg (= S193). The Balmer lines exhibit broad, asymmetric wings Doppler-shifted by about 2000 km/s at the edges, while the HeI lines show phase-dependent absorption features strikingly similar to SW Sextantis stars, as well as emission through most of the phase. The CIII/NIII emission blend does not show any phase dependence. From velocities of Halpha emission lines, we determine an orbital period of 0.174774 +/- 0.000003 d (= 4.1946 h), which agrees with Szkody's (1995) value of approximately 4.2 hours. …
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 a…
We report on a discovery of unexpected activities in two X-ray bright dwarf novae. GZ Cnc showed an anomalous clustering of outbursts in 2002, in contrast to a low outburst frequency in the past record. The activity resembles an increased activity seen in some intermediate polars or candidates. We identified NSV 10934, X-ray selected high-amplitude variable star, as a dwarf nova with unusually rapid decline. The outburst characteristics make NSV 10934 a twin of recently discovered intermediate polar (HT Cam) with dwarf nova-type outbursts. We propose that these activities in X-ray strong dwarf…
We present spectroscopy of 15 star-forming BzK galaxies (sBzKs) with K(AB)<23 in the Subaru Deep Field, for which Halpha and some other emission lines are detected in 0.9 to 2.3 micron spectra with a resolution of R=500. Using Halpha luminosities, we obtain star formation rates (SFRs), and then specific SFRs (SSFRs) dividing SFRs by stellar masses, which are derived from SED fitting to BVRi'z'K photometry. It is found that sBzKs with higher stellar masses have larger SFRs. A negative correlation is seen between stellar mass and SSFR, which is consistent with the previous results for z~2 galaxi…
The 2dF QSO survey is a spectroscopic survey of 48,000 point-sources selected by colour with magnitudes in the range 18.35 < B < 20.95. Amongst QSOs, white dwarfs, narrow-line galaxies and other objects are some cataclysmic variables (CVs). This survey should be sensitive to intrinsically faint CVs. In the standard picture of CV evolution, these form the majority of the CV population. We present the spectra of 6 CVs from this survey. Four have the spectra of dwarf novae and two are magnetic CVs. We present evidence that suggests that the dwarf novae have period P < 2 h and are indeed intrinsic…
We present high- and medium-resolution spectroscopic observations of the cataclysmic variable BF Eri during its low and bright states. The orbital period of this system was found to be 0.270881(3) days. The secondary star is clearly visible in the spectra through absorption lines of the neutral metals MgI, FeI and CaI. Its spectral type was found to be K3+-0.5. A radial velocity study of the secondary yielded a semi-amplitude of K_2=182.5+-0.9 km/s. The radial velocity semiamplitude of the white dwarf was found to be K_1=74+-3 km/s from the motion of the wings of the Halpha and Hbeta emission …
Aims: We present discovery observations of the new cataclysmic variable star (CV) 1RXS J092737.4-191529, as well as spectra and photometry of SY Vol. The selection technique that turned up these two CVs is described; it should be efficient for finding dwarf novae with high outburst duty cycles. Methods: Two very common observational features of CVs, namely optical variability and X-ray emission, are combined to select targets for follow-up observations. Long-slit spectra were taken to identify CVs in the sample. Results: Two out of three objects selected in this way are CVs. One of these is th…
We report the results of a spectropolarimetric survey of a complete far infrared selected sample of Seyfert 2 galaxies. We have found polarized broad Halpha emission in one new source, NGC5995. In the sample as a whole, there is a clear tendency for galaxies in which we have detected broad Halpha in polarized light to have warm mid--far infrared colours (F(60um)/F(25um)<4), in agreement with our previous results. However, a comparison of the optical, radio and hard x-ray properties of these systems leads us to conclude that this is a secondary consequence of the true mechanism governing our ab…
We present the latest catalog of more than 1200 spectroscopically-selected close binary systems observed with the Sloan Digital Sky Survey through Data Release Five. We use the catalog to search for magnetic white dwarfs in cataclysmic variable progenitor systems. Given that approximately 25% of cataclysmic variables contain a magnetic white dwarf, and that our large sample of close binary systems should contain many progenitors of cataclysmic variables, it is quite surprising that we find only two potential magnetic white dwarfs in this sample. The candidate magnetic white dwarfs, if confirme…
Some magnetic CVs like BY Cam are characterized by unusual CNO line ratios compared to other polars and non-solar abundances have been suggested to explain this anomaly. We present here a first attempt to constrain the elemental abundances in these systems by applying a specific ionisation model combined with a geometrical description of the accretion column where these lines are thought to be formed. The line luminosities have been computed using the CLOUDY plasma code for different ionisation spectra and column extension. We show here selected results and compare to the values observed in "p…
[Abridged] We present here a new and homogeneous sample of 3340 galaxies selected from the Sloan Digital Sky Survey (SDSS) based solely on the observed strength of their Hdelta absorption line. These galaxies are commonly known as ``post-starburst'' or ``E+A'' galaxies, and the study of these galaxies has been severely hampered by the lack of a large, statistical sample of such galaxies. In this paper, we rectify this problem by selecting a sample of galaxies which possess an absorption Hdelta equivalent width of EW(Hdelta_max) - Delta EW(Hdelta_max) > 4A from 106682 galaxies in the SDSS. We h…
Using a recently completed survey of faint (sub-mJy) radio sources, selected at 1.4 GHz, a dust-free estimate of the local star formation rate (SFR) is carried out. The sample is 50% complete to 0.2 mJy, with over 50% of the radio sources having optical counterparts brighter than R = 21.5. Spectroscopic observations of 249 optically identified radio sources have been made, using the 2-degree Field (2dF) facility at the Anglo-Australian Telescope (AAT). Redshifts and equivalent widths of several spectral features (e.g., Hαand [OII]3727) sensitive to star formation have been measured and used to…
We report follow-up observations of a new white dwarf/red dwarf binary HS2237+8154, identified as a blue variable star from the Hamburg Quasar Survey. Ellipsoidal modulation observed in the R band as well as the Halpha radial velocity variations measured from time-resolved spectroscopy determine the orbital period to be Porb=178.10+-0.08min. The optical spectrum of HS2237+8154 is well described by a combination of a Teff=11500+-1500K white dwarf (assuming log g=8) and a dM3.5+-0.5 secondary star. The distance implied from the flux scaling factors of both stellar components is d=105+-25pc. Comb…
We present high-speed, three-colour photometry of the eclipsing cataclysmic variable SDSS J150722.30+523039.8 (hereafter SDSS J1507). This system has an orbital period of 66.61 minutes, placing it below the observed ``period minimum'' for cataclysmic variables. We determine the system parameters via a parameterised model of the eclipse fitted to the observed lightcurve by chi^2 minimisation. We obtain a mass ratio of q = 0.0623 +/- 0.0007 and an orbital inclination i = 83.63 +/- 0.05 degrees. The primary mass is M_w = 0.90 +/- 0.01 M_sun. The secondary mass and radius are found to be M_r =0.05…
The radio source FIRST J102347.6+003841 was presented as the first radio-selected cataclysmic. In the discovery paper, Bond et al. (2002) show a spectrum consistent with a magnetic AM Her-type system and a light curve with rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius (2004) found a smoothly-varying light curve with a period near 4.75 h and one minimum per orbit, indicating a dramatic change. We present time-resolved spectra showing a superficially normal, mid-G type photosphere, with no detectable emission lines. The absorption-line radial velocity varies sinusoidally…
We present integrated H alpha measurements obtained from imaging observations of 98 late-type galaxies, primarily selected in the Coma supercluster. These data, combined with H alpha photometry from the literature, include a magnitude selected sample of spiral (Sa to Irr) galaxies belonging to the "Great Wall" complete up to mp=15.4, thus composed of galaxies brighter than Mp=-18.8 (H0=100 km Mpc^-1 s^-1). The frequency distribution of the H alpha E.W., determined for the first time from an optically complete sample, is approximately gaussian peaking at E.W. ~25 A. We find that, at the present…
We present further spectroscopic observations for a sample of galaxies selected in the vacuum ultraviolet (UV) at 2000 Åfrom the FOCA balloon-borne imaging camera of Milliard et al. (1992). This work represents an extension of the initial study of Treyer et al. (1998). Our enlarged catalogue contains 433 sources; 273 of these are galaxies, nearly all with redshifts z=0-0.4. Nebular emission line measurements are available for 216 galaxies, allowing us to address issues of reddening and metallicity. The UV and Halpha luminosity functions strengthen our earlier assertions that the local volume-a…
We give an identification summary and results of polarimetric, photometric and spectroscopic follow-up observations of new, X-ray bright cataclysmic variables. These were identified as optical counterparts of high galactic latitude sources in the ROSAT All-Sky Survey. This optical identification programme is termed the ROSAT Bright Survey (RBS) and represents the first complete soft X-ray selected, flux-limited sample of CVs at high galactic latitude (survey area ~20400 sq.deg.). The systems described here escaped previous identification programmes since these surveys were designed to identify…
Barnes-Evans type relations provide an empirical relationship between the surface brightness of stars and their color. They are widely used for measuring the distances to stars of known radii, as the Roche-lobe filling secondaries in cataclysmic variables (CVs). The calibration of the surface brightness of field dwarfs of near-solar metalicity with spectral types A0 to L8 covers all secondary spectral types detectable in CVs and related objects and will aid in the measurement of their distances. The calibrations are based on the radii of field dwarfs measured by the Infrared Flux Method and by…
Blue- and red-shifted Hydrogen and Helium satellite recombination lines have recently been discovered in the optical spectra of at least two supersoft X-ray sources (SSSs), RX J0513-069 and RX J0019.8+2156, and tentatively also in one short-period cataclysmic variable star (CV), the recurrent nova T Pyx. These features are thought to provide evidence for the presence of highly collimated jets in these systems. No similar spectral signatures have been detected in the spectra of other short-period CVs. Here, we ask if this apparent absence of ``jet lines'' in the spectra of most CVs already impl…
We present time-resolved optical spectroscopy and photometry of four relatively bright (V~14.0-15.5) long-period cataclysmic variables (CVs) discovered in the Hamburg Quasar Survey: HS0139+0559, HS0229+8016, HS0506+7725 and HS0642+5049. Their respective orbital periods, 243.69+-0.49min, 232.550+-0.049min, 212.7+-0.2min and 225.90+-0.23min are determined from radial velocity and photometric variability studies. HS0506+7725 is characterised by strong Balmer and He emission lines, short-period (~10-20min) flickering and weak X-ray emission in the ROSAT All Sky Survey. The detection of a deep low …
We study the large-scale spatial distribution of low-redshift quasars and Seyfert~1 galaxies using a sample of 106 luminous emission-line objects ($\bar{M}_{B} \approx -23$) selected by their H$α$ emission lines in a far-red objective prism survey ($0.2 < z < 0.37$). Of the 106 objects, 25 were previously known AGN (Veron-Cetty and Veron 2000), and follow-up spectroscopy for an additional 53 objects (including all object pairs with separation $r < 20 \hmpc$) confirmed 48 AGN and 5 narrow emission-line galaxies (NELGs). The calculated amplitude of the spatial two-point correlation function for …
Cataclysmic variables (CVs) are tracers of dynamical evolution in globular clusters. A significant sample has been found by the relatively shallow \Halpha surveys conducted with HST thus far in just three globulars: NGC 6397 (3), NGC 6752 (2), and $ω$-Cen (2). These are identified with the low luminosity x-ray sources discovered in these globulars with similarly moderate-depth ROSAT surveys. Follow-up spectroscopy of the initial 3 CV candidates in NGC 6397 with the FOS on HST suggests they may be magnetic CVs of the intermediate polar (IP) type, and follow-up deep imaging with both HST and ROS…
The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects emission line galaxies by a scan with an imaging Fabry-Perot interferometer. It covers 5 fields of > 100 square arcmin each in three wavelengths windows centered on lambda ~ 700, 820, and 920nm, and reaches to a typical limiting line flux of 3 x 10^(-20) W m^(-2). This is the deepest emission line survey covering a field of several 100 square arcmin. Galaxies between z = 0.25 and z = 1.4 are detected by prominent emission lines (from Halpha to [OII]372.7) falling into the FP scans. Additional observations with a…
The cross-correlation between the ROSAT all-sky survey (~150000 sources) and the Tycho mission (~1000000 stars) catalogs has selected about 14000 stellar X-ray sources (RasTyc sample, Guillout et al. 1999). About 200-300 stars have been spectroscopically observed at high resolution both in the Halpha and LiI lambda-6708 regions with Elodie and Aurelie spectrographs of the OHP (Observatoire de l'Haute Provence, France). The aim was to classify the RasTyc star sample in terms of age and chromospheric activity level and to detect eventual binary systems. Photometric and spectroscopic follow-up ob…
