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Uva-DARE (Digital Academic Repository) UvA-DARE (Digital Academic Repository) Photometric observations of faint cataclysmic variables Howell, S.B. Publication date 1995 Link to publication Citation for published version (APA): Howell, S. B. (1995). Photometric observations of faint cataclysmic variables. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:25 Sep 2021 Chapterr 6 CCDD Time Resolved Photometry of Faintt Cataclysmic Variables IV S.. B. Howell, P. Szkody. T. Kreidl. and D. Dobrzycka Publ.Publ. of the Ast. Soc. of the Pac. 1991, 103, 300 ABSTRACT T Wee observed fifteen faint stars, known or suspected to be cataclysmic variables, obtaining ('CDD time resolved photometry in V', B, and the near-1R. The stars are: \VX Cet, CP Eri. XZZ Eri. V592 Her, TT Ind, AO Oct, BE Oct. CT Ser. V227G Sgr. KK lei. DR CMa. R\V EMi,, PG0917+342, PG2240+19:Ï, and 2138 - 15:5. All of the stars were observed for - 2 or moree hours, with the average time series length being over 3 hours. We find orbital periods forr the stars KK Tel and 2138 — -1-r>;3 and a likely period confirmation for RW EMi. ('I' Eri iss a probable DQ Her star, showing an optical modulation of 29 minutes. Nine other stars showw photometric evidence which likely confirms them as cataclysmic variables, while Un- truee natures of PG0917+342 and PG224Ü+193 are not yet revealed. 6.11 Introduction Thiss paper is the fourth in a series of our continuing project to obtain ('CD time resolved photometryy of faint cataclysmic variables (CVs) (Paper I: Howell and Szkody 19N8; Paper II:: Szkody et at. 1989: Paper III: Howell et al. 1990). Cataclysmic variables (CVs) are 99 9 100 0 ('CD('CD Time-Resolved Photometry of Faint CVs closee binaries in which a mass-losing secondary (a late main-sequence dwarf) is in orbit with aa white-dwarf primary. Typical dimensions for these systems are of the order of a solar diameter,, and accordingly they have periods that are very short; a little over 1 hr to about. 155 hours. The material that is lost from the secondary usually accumulates in a disk around 11 he primary with eventual accretion onto its surface. This transfer of material to the disk can bee responsible for flickering (random low-level variations of order 0.1-1.0 mag), and periodic variationss due to viewing the hot spot created at the stream/disk interface. An increase in thee transfer rate of material from the secondary to the disk, or a disk instability leading too increased transfer of material through the disk, is thought to be the cause of the usual 2-55 mag outbursts observed in the dwarf novae type of CVs (see the review by Wade and Wardd 1985). All dwarf novae with periods below the period gap show, at times, enhanced outburstss called superouthursts. During the superoutbursts. there are photometric humps presentt at a period a few percent longer than the orbital period. These stars belong to a subgroupp of CVs known as the SI Crsae Majoris stars (reviewed by Warner 1985). Thee stars we observe in this continuing project generally have little or no previous informationn other than some hint of being likely candidates for CVs. The goals of obtaining ('CDD photometry on such binaries and determining their colors are 1) to search for variability andd periodicities related to the orbital periods and the spin periods of magnetic white dwarfs; andd 2) to look for long- term changes in the quiescent properties of these stars (see Paper 111). Thee major focus of this study is on stars with evidence for short periods (less than 4 hours), andd CVs that an1 at high galactic latitudes as described in Howell and Szkody (1990). Other faintt unstudied and/or interesting systems are also included. Detailed analysis of interesting systemss and synthesis of our collected data are published separately. ('singg ('CDs as our detectors, we can gather time series data with one to ten-minute timee resolutions for stars from ~ 14 magnitude down to magnitude 20-22 with 1-2 meter classs telescopes. For the faintest stars (V' > 17 — 18) we are usually providing the lirst such dataa available. Papers 1 through IV contain data on a total of 52 stars and over 100 time seriess dat a sets. 6.22 Observations Thee data presented here were obtained with the Perkins 1.8-m telescope of the Ohio Statee and Ohio Wesleyan Universities at the Lowell Observatory, the Kitt Peak National Observatoryy No. 1 0.9-m telescope, and the Cerro Tololo Inter-American Observatory 0.9- mm telescope. The data from Kitt Peak and CTIO were reduced either with the "cdphot" packagee available on the instrument computer at the telescope or with the APPHOT package 6.3.6.3. RESULTS 101 1 inn 1RAF '. The Lowell data were reduced with the IRAF/APPfIOT package. Table (U gives ann observing log for the data presented here. Ourr general observing policy for these types of data is to observe a few photometric standardss each night to determine rough offsets between instrumental and real magnitudes. Wee obtain single color measurements directly before or after our time series data. The standardss are then used to give the average magnitude values listed in Table (i.1. with an errorr of ~ 1 mag. The time series data sets were reduced and have their errors determined ass given in Howell e.t al. (1988). Alll the data sets were searched for periodic modulations using the technique of Phase Dispersionn Minimization (yield) developed by Stellingwerf (1978). The PDM technique pro- videss the user with a test statistic for eacli determined period that yields a confidence level viaa an (two-sided) F-test, We indicate that, no periods were seen if our PDM analysis fails too reveal any period at all with a confidence level of > 70 - 80%. Between ~ 80% and 90% confidencee level (CL), we generally will mention the result, as it may possibly be of some interestt or get confirmed later. We define a period to be real if it gives an acceptable (usually >> 9')%.) confidence level, and we believe it to be stable if it is seen on more than one night at thiss high OL. Table 6.2 gives a list of the periods seen in our l-r) stars from this paper which falll into the L'real and stable'' category. Many CVs do, however, show nightly changes in averagee magnitude level and flickering characteristics, which may lead to erroneous "periods" beingg determined. The less confident periods, that may or may not be real, are listed in the individuall discussion for each star presented in the next section. 6,33 Results 6.3.11 WX Ceti Paperr II presented our initial work on this star. A possible period of 5 minutes (inn the near-IR) was seen, but with low confidence since the data set length was short. We presentt here two new data sets taken in V and B (see Figure (i.1). Our V' data set shows no indicationn of any periods and shows simply a flickering light curve. Our B data set. however, showss indications of periods at 8 and 7 min. These periods are at confidence [RAFF is distributed by National Optical Astronomy Observatories, which is operated by the Association off 1'niversitios for Research in Astronomy. Inc., under cooperative agreement with the National Science Foundation n 102 2 CCDCCD Time-Resolved Photometry of Faint CVs Tab lbee 6.1: Observing gLo g g Star r ITT Dato ITT Start" N'1 1 C Cdt 6 6 TTh h CCDr r Filter" " Mag' ' ^ ^ \VXX (Vi OlSepSO O 08:29:13 3 60 0 180 0 23 3 3.4 4 TI6 6 B B 17.8 8 0.02 2 08:28:40 0 V V 17.6 6 03Xov89 9 06:16:40 0 29 9 300 0 13 3 2.5 5 RCA A V V 17.7 7 0.03 3 (TT Eri 04Sep89 9 09:16:37 7 30 0 320 0 23 3 2.9 9 TI6 6 B B 19.3 3 0.05 5 09:12:30 0 V V 19.7 7 26Aug90 0 08:25:56 6 21 1 300 0 29 9 1.9 9 TI3 3 V V 19.8 8 0.03 3 XZZ Eri 04Xov89 9 08:14:20 0 55 5 220 0 13 3 3.8 8 RCA A V V 18.7 7 0.06 6 V5922 Her 20Apr90 0 09:06:10 0 15 5 400 0 13 3 1.7 7 RCA A \VR R 0.10 0 09:05:20 0 V V 20.5 5 Trrr Ind 277 Aug!)» 00:50:14 4 100 0 120 0 29 9 4.1 1 TI3 3 V V 0.12 2 23:52:00 0 B B 16.8 8 23:58:00 0 V V 16.6 6 28Aug90 0 00:01:00 0 R R 16.1 1 AC)) Oct 25Aug90 0 04:10:11 1 10 0 360 0 29 9 1.1 1 T13 3 V V 21.1 1 0.14 4 03:42:18 8 B B 21.0 0 03:55:00 0 V V 20.9 9 04:02:00 0 R R 20.7 7 23:44:33 3 R R 20.2 2 23:51:38 8 V V 20.9 9 23:58:34 4 B B 20.6 6 26Aug90 0 00:06:37 7 37 7 360 0 29 9 4.0 0 TI3 3 V V 20.9 9 0.09 9 BEE Oct.
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