Dartmouth College Dartmouth Digital Commons Open Dartmouth: Published works by Dartmouth faculty Faculty Work 10-1-2001 Spectroscopy and Orbital Periods of Four Cataclysmic Variable Stars John R. Thorstensen Dartmouth College Cynthia J. Taylor Dartmouth College Follow this and additional works at: https://digitalcommons.dartmouth.edu/facoa Part of the Stars, Interstellar Medium and the Galaxy Commons Dartmouth Digital Commons Citation Thorstensen, John R. and Taylor, Cynthia J., "Spectroscopy and Orbital Periods of Four Cataclysmic Variable Stars" (2001). Open Dartmouth: Published works by Dartmouth faculty. 1868. https://digitalcommons.dartmouth.edu/facoa/1868 This Article is brought to you for free and open access by the Faculty Work at Dartmouth Digital Commons. It has been accepted for inclusion in Open Dartmouth: Published works by Dartmouth faculty by an authorized administrator of Dartmouth Digital Commons. For more information, please contact [email protected]. Mon. Not. R. Astron. Soc. 326, 1235–1242 (2001) Spectroscopy and orbital periods of four cataclysmic variable stars John R. ThorstensenP and Cynthia J. Taylor Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA Accepted 2001 May 2. Received 2001 May 2; in original form 2001 March 29 ABSTRACT We present spectroscopy and orbital periods Porb of four relatively little-studied cataclysmic variable stars. The stars and their periods are: AF Cam, Porb ¼ 0:324ð1Þ d (the daily cycle count is slightly ambiguous); V2069 Cyg (¼ RX J2123.714217), 0.311683(2) d; PG 09351075, 0.1868(3) d; and KUV 0358010614, 0.1495(6) d. V2069 Cyg and KUV 0358010614 both show He II l4686 emission comparable in strength to Hb. V2069 Cyg appears to be a luminous nova-like variable, and the strong He II suggests it may be an intermediate polar. The period of KUV 0358010614 is similar to members of the SW Sex- type nova-like variables, and it shows the phase-dependent absorption in the Balmer and He I lines typical of this subclass. AF Cam shows absorption features from a K-type secondary, as expected given its rather long orbital period. The secondary spectrum and the outburst magnitude both suggest that AF Cam is approximately 1 kpc distant. The spectrum of PG 09351075 resembles that of a dwarf nova at minimum light, with a noticeable contribution from an M-dwarf secondary star. The secondary spectrum and a tentative outburst magnitude both suggest a distance near 500 pc. Key words: binaries: close – stars: fundamental parameters – novae, cataclysmic variables – stars: variables: other. 1 INTRODUCTION 2 TECHNIQUES Cataclysmic variable stars (CVs) are close binary systems in which All the observations (summarized in Table 1) are from the MDM a red dwarf transfers matter on to a white dwarf, generally by Observatory on Kitt Peak, Arizona. The 1998 January observations overflowing its Roche critical lobe. Warner (1995) gives an of KUV 0358010614 are from the 1.3-m McGraw-Hill telescope excellent comprehensive review of CVs. and Mark III spectrograph, and all others are from the 2.4-m The orbital period of a cataclysmic is a fundamental observable Hiltner telescope and modular spectrograph. We observed which correlates with evolutionary state and outburst type. In comparison lamps frequently, and checks of the l5577 night-sky addition, the Ritter & Kolb (1998) catalogue, which is heavily used line show that our wavelength scale is typically stable to by the CV community, includes only those systems with known or ,10 km s21. When the weather appeared photometric, we observed suspected binary periods, with the result that a system remains flux standards in twilight. Even so, our absolute fluxes are not largely ‘beneath the radar’ until a period is measured. Photometry expected to be accurate to much better than 30 per cent, because of yields incontrovertible orbital periods when eclipses are present, occasional clouds and variable losses at the spectrograph slits but other modulations can masquerade as orbital periods. Radial- (1 arcsec at the 2.4 m, 2.2 arcsec at the 1.3 m). Furthermore, for velocity spectroscopy is therefore the most reliable technique for unknown reasons the modular spectrograph produces wavelike determining orbital periods of non-eclipsing CVs. The long distortions in the continua; these appear to average out in sums of cumulative exposures needed to find reliable periods are useful for many exposures. Table 2 contains measurements of the average characterizing the stars in other ways as well. fluxed spectra. We present here spectra and radial velocity periods for four CVs. The data were reduced to counts versus wavelength at the 1 Section 2 details the techniques common to the studies, Section 3 observatory, using standard procedures within IRAF. Radial gives background information and results for the individual stars, velocities of emission lines were measured using convolution and Section 4 contains a brief discussion. algorithms described by Schneider & Young (1980) and Shafter 1 IRAF, the Image Reduction and Analysis Facility, is distributed by the National Optical Astronomy Observatories, under contract to the US PE-mail: [email protected] National Science Foundation. q 2001 RAS Downloaded from https://academic.oup.com/mnras/article-abstract/326/4/1235/1062341 by Dartmouth College Library user on 25 April 2018 1236 J. R. Thorstensen and C. J. Taylor Table 1. Observing log. Run Nights N exposure Range Dl (s) (A˚ )(A˚ ) V2069 Cyg 1997 September 3 23 360 4000–7500 3.7 1997 December 3 12 480 4000–7500 3.7 1998 September 1 3 480 4040–7500 3.7 1999 June 3 9 300 4230–7580 3.6 1999 October 4 7 240 4230–7550 3.9 AF Cam 2000 January 5 32 360 4210–7560 3.6 PG 09351075 1996 April 3 27 480 4208–6780 2.7 2000 January 4 21 480 4210–7560 3.6 KUV 0358010614 1997 December 3 41 480 4000–7500 3.7 1998 January 4 7 900 4845–6865 4.5 1999 October 4 57 480 4230–7560 3.6 Exposure times listed are typical values for each run. Dl is the FWHM resolution determined from fits to night-sky features. (1983). For absorption velocities, we used the cross-correlation was possible for M0. The secondary contribution was 30–40 per algorithms of Tonry & Davis (1979), as implemented in the RVSAO cent of the light near l6500. For the secondary alone we find package (Kurtz & Mink 1998). To search for periods we used the V ¼ 18:4, with an uncertainty estimated from the decomposition ‘residual-gram’ method described by Thorstensen et al. (1996), and and the flux calibration of perhaps ^0.5 mag. to test alias choices in doubtful cases we used the Monte Carlo We cross-correlated the ll5020–5860 and ll5900–6500 method explained by Thorstensen & Freed (1985). With the rough regions against a composite of several G- and K-type IAU radial period established, we fit the velocities with sinusoids, the velocity standards, and obtained velocities for 30 of our 32 target parameters of which are in Table 3. spectra, with typical estimated errors ,20 km s21. We measured We note one simple innovation in these otherwise standard the Ha emission line by convolving with the derivative of procedures. As part of the spectral reduction process, IRAF can Gaussian, optimized for a 16 A˚ FWHM. The counting-statistics estimate the noise in each spectral bin from the readout noise, velocity uncertainties here were typically 10 km s21. Fig. 2 shows detector gain, background, and so on. We have modified the periodograms for the emission and absorption velocities, both of convolution algorithm to compute a counting-statistics uncertainty which favour a period near 0.32 d, but with the inevitable daily in the radial velocities by propagating these noise estimates cycle-count aliases. The Monte Carlo tests give discriminatory through the calculation. These a priori estimates allow the data to powers (defined in Thorstensen & Freed 1985) of 0.96 and 0.83 for be more optimally weighted in period finding and curve fitting. the emission and absorption time series respectively, with correctness likelihoods somewhat higher than this, so the cycle count is reasonably secure, but frequencies differing by 1 cycle d21 3 THE INDIVIDUAL STARS cannot be excluded absolutely. The data span 7.8 h of hour angle, ordinarily enough to decide daily cycle counts unambiguously, but 3.1 AF Camelopardalis the sampling is somewhat sparse and the period is awkwardly close This object is listed in the General Catalog of Variable stars to an integer submultiple of one day. On the face of it, Szkody & (Kholopov et al. 1988) as a U Gem-type dwarf nova with Howell’s (1989) 5–6 h period favours the ,4 cycle d21 alias, rather 21 13:4 # mpg # 17:6. It is the only star here with a useful period than the ,3 cycle d we adopt; however, their data do not have estimate in the literature. Early indications of a very short period enough hour angle span to influence the choice. (Szkody & Mateo 1986, Howell & Szkody 1988) prompted an Fig. 3 shows the velocities folded on the combined best period. emission-line radial velocity study by Szkody & Howell (1989). The sine fits (Table 3) show that the emission-line velocity They obtained very limited data which indicated a 5–6 h period, modulation lags the absorption-line velocities by 0:54 ^ 0:02 leading Ritter & Kolb (1998) to tabulate Porb ¼ 0:23: in their cycles, suggesting as usual that the emission lines do not trace the catalogue. white dwarf motion with any precision. We observed this object in 2000 January, in quiescence. The The secondary velocity amplitude suggests a fairly low orbital mean spectrum (Fig. 1) shows the absorption features of a late-type inclination, as might be expected from the single-peaked emission 21 secondary star, as would be expected given the relatively long Porb.