COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2029 Konkoly Observatory Budapest 1981 October 22 HU ISSN 0374-0676 TU Men, THE FIRST SU UMa STAR BEYOND THE GAP* In December 1980, TU Men was detected to be a member of the SU UMa subgroup of dwarf novae (Stolz, Schoembs, 1981). Now, spectra of TU Men revealed an orbital period beyond the wellknown gap between 2 and 3 hours as has been suspected from the superhump period P_s~= 3h. Spectroscopy of TU Men has been performed in 4 nights during the superoutburst in Dec. 1980 with the IDS at the 1.5m telescope at ESO. Table I Journal of observations Date covered time Dispersion number of spectra interval (A/mm) (20min Int.-time) (JD-2444500) --------------------------------------------------------------- 1980-11-30/1 74.5661-74.7190 39 8 1980-12-01/2 75.5264-75.8230 114 16 1980-12-02/3 76.5330-76.6836 114 9 1980-12-03/4 77.5264-77.6709 114 9 --------------------------------------------------------------- All spectra show the typical very broad Balmer absorption lines of dwarf novae during outburst. For determination of the orbital period the spectra have been smoothed and the radial velocity for each clearly detectable Balmer absorption line has been measured. A sinus curve has been fitted to the mean velocities of each spectrum. The minimum of rms-error is obtained for the period P_0 = 2.823 hours +-17 *Based on observations collected at the European Southern Observatory, La Silla, Chile. The ephemerides for the upper conjunction are HJD (up.conj.) = 2 444 574.561d + .1176d. E +-7 +-7 Figure 1 shows the resulting phase diagram. Including TU Men and WZ Sge orbital and superhump periods are known for 7 objects until now. Figure 2 shows the relation of (P_s - P_0)/P_0 versus P_s for these stars. The values fit quite well to a parabola; the order of the fit is not very significant however. [FIGURE 1] Fig. 1. Radial velocity curve of TU Men obtained during the superoutburst in December 1980. Using this relation orbital periods for SU UMa objects with P_s known only can be calculated. Table II shows the results. Table II ------------------------------------------ Star P_s(d) Lit. computed P_0(d) ------------------------------------------ EK TRA .06492 (1) .0636 AY LYR .07552 (2) .0730 CU VEL .07990 (3) .0769 YZ CNC .09204 (2) .0876 ------------------------------------------ References (1) Vogt and Semeniuk, 1980 (2) Patterson, 1979 (3) Vogt, 1981 [FIGURE 2] Fig. 2. (Ps-P0)/P0 versus P0 for seven objects with known orbital and superoutburst period. The values for P0 and Ps have been taken from the following references: WZ Sge - Patterson et al., 1981 V 436 Cen - Vogt, 1981; Semeniuk, 1980 CY Car - Vogt, 1981; Vogt et al., 1981 VW Hyi, WX Hyi, Z Cha - Vogt, 1980 The orbital period of TU Men and the calculated orbital period of YZ Cnc diminish the period gap of cataclysmic variables to 40 minutes. B. STOLZ R. SCHOEMBS Universitats- Sternwarte Scheinerstr. 1 D-8000 Munchen 80 Germany References: Patterson, J., 1979, Astron. J. 84, 804 [BIBCODE 1979AJ.....84..804P ] Patterson, J., McGraw, J.T., Coleman, L., Africano, J.L., 1981, Astrophys. J. 248, 1067 [BIBCODE 1981ApJ...248.1067P ] Semeniuk, J., 1980, Astron. Astrophys. Suppl. 39, 29 [BIBCODE 1980A&AS...39...29S ] Stolz, B., Schoembs, R., 1981, Inf. Bull. Var. Stars, No. 1955 Vogt, N., Semeniuk, J., 1980, Astron. Astrophys. 89, 223 [BIBCODE 1980A&A....89..223V ] Vogt, N. 1980, Astron. Astrophys. 88, 66 [BIBCODE 1980A&A....88...66V ] Vogt, N., Schoembs, R., Krzeminski, W., Pedersen, H., 1981, Astron. Astrophys. 94, L29 [BIBCODE 1981A&A....94L..29V ] Vogt, N., 1981, Habilitationsschrift, Ruhr-Universitat Bochum [BIBCODE 1981susu.book.....V ]