From owner-vsnet-adm@kusastro.kyoto-u.ac.jp Sat Dec 20 22:05 JST 1997 Date: Sat, 20 Dec 1997 08:05:03 -0500 From: "John R. Thorstensen" <thorsten@Dartmouth.EDU> To: vsnet-adm@kusastro.kyoto-u.ac.jp Reply-To: vsnet-adm@kusastro.kyoto-u.ac.jp X-Sequence: vsnet-adm 3402 Subject: Orbital period of RX J0757.0+6306 Sender: owner-vsnet-adm@kusastro.kyoto-u.ac.jp Content-Type: text Content-Length: 2225 Hello VSNetters, Gaghik Tovmassian (UNAM) recently called attention to RX J0757.0+6306, for which he quoted a most likely orbital period of 81 +- 5 minutes (vsnet-chat number 663). The object has very strong H emission and he noted the similarities with WZ Sge (another very short-period, strong-lined cataclysmic). In addition the object showed 8.5-minute oscillations in its light curve on several occasions, suggesting the possibility of a DQ Her classification. I obtained spectra of this remarkable object on December 18 and 19 UT, using the MDM 2.4-m telescope and modular spectrograph, at 3 A FWHM resolution from 4000 to 7500 Angstroms. The hydrogen lines are indeed extremely strong, with H-alpha having an equivalent width of about 200 Angstroms. HeII 4686 is not unusually strong, with an equivalent width of 13 A, about 1/10 the strength of H-beta. The strong H lines made it possible to measure good radial velocities in this object, for which I guesstimate a magnitude well fainter than 17 (see Bob Fried's observations reported below). Discarding a few weakly-exposed spectra taken through moonlit clouds left 67 exposures of 6 minutes each. The spectra covered a 6.79 hour range of hour angle. The radial velocities of the emission lines define an unambiguous period 0.05982 +- 0.00013 days, or 86.14 +- 0.19 minutes. The radial-velocity curve on this period is fairly clean (amplitude/scatter = 2.8). While daily cycle-count aliases are present in the periodogram, they are weak and symmetrically distributed around the main peak. If the weather clears tonight, I may be able to decrease the ncertainty slightly. This period is at the upper end of Tovmassian's quoted range. In addition, Joe Patterson (Columbia U.) passes on the following: Robert Fried, Braeside Observatory, observed the star photometrically for 7-hour runs on December 16 and 17. The star was near magnitude 18, and no significant periodicity was seen (to a limit of 0.07 mag) near the range of a possible orbital period (1-4 hr). However, a significant signal was detected at 515.1+-0.3 s, with a full amplitude of 0.06 mag. John Thorstensen Department of Physics and Astronomy Dartmouth College