COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4043 Konkoly Observatory Budapest 30 June 1994 HU ISSN 0374 - 0676 OUTBURST OBSERVATIONS OF LL ANDROMEDAE LL Andromedae is an obscure object listed in the General Catalogue of Variable Stars as a possible U Gem star with a magnitude range of 13 to fainter than 17th. Wild (1979) reported the discovery of this object during which the star was seen to brighten to m_pg ~13th and appeared to fade after about 10 days, although it was very poorly sampled. On 1993 Dec 07, LL And went into outburst and this note briefly describes our observations. T. Vanmunster reported a rare outburst of LL And on 1993 Dec 7. This was quickly confirmed by G. Poyner and P. van Canteren and reported in Vanmunster and Poyner (1993). Figure 1 shows the outburst light curve of LL And as gathered from various observers. We see that the rise was very fast (<0.5 days) while the decline was slower, the outburst itself lasting about 8 days. The minimum magnitude of LL And is estimated to be near V~20+/-0.5 on the POSS O plate. The maximum V magnitude reached was 13.8+/-0.1, thus giving LL And an outburst amplitude of ~6 magnitudes. A precise position for LL And is RA=00h39m11.90s DEC=+26d20'54.9" [1950]. Spectroscopic observations of LL And were made on UT 1993 Dec 8 and 9, both when LL And was near maximum at V~14th magnitude. Our spectra show the Balmer Series and He 5876 as weak absorption lines, all with possible emission cores. Our spectra also show a rising blue continuum indicative of a DN in outburst. Kato (1993) reported his discovery of superhumps in LL And from observations taken over a four-night period. He calculated a superhump period of 0.057006 days (1.37 hrs), one of the shortest known. In Table 1 we extend the tabulation of superhump periods given by Molnar and Kobulnicky (1992) with additional systems from the literature. We use all the stars with both orbital and superhump periods measured to derive a linear expression relating the two periods (periods given in days): P_SH = 1.06577(+/-0.01457)P_0 - 0.00160(+/-0.01564) Note that this expression predicts that the superhump period and orbital period have a constant offset, regardless of orbital period. This simple approach provides observers with a fairly accurate starting point when looking for either period, if the other is known. It also fits all the known data to 1.5% as well. Figure 2 shows the results of this fit for the data in Table 1. Applying this equation to Kato's superhump period of LL And, we calculate an orbital period of 1.32 hours (79 minutes). This period is very close to the minimum orbital period allowed (~72 min) by theory for solar composition stars (Nelson et al. 1985). [FIGURE 1] Figure 1. The outburst light curve of LL And. Open triangles are upper limits and filled squares have errors of ~+-0.1 mags. [FIGURE 2] Figure 2. Linear relation between superhump period and orbital period. Table 1 Short Period Dwarf Novae with Orbital and Superhump Periods^1 P_O P_SH Name (days) (days) WZ Sge 0.0567 0.0571 SW UMa 0.0568 0.0583 T Leo 0.0588 0.0641 HV Vir 0.0580 0.0584 VY Aqr 0.0600 0.0645 V436 Cen 0.0625 0.0638 OY Car 0.0631 0.0642 TY Psc 0.0639 0.0701 IR Gem 0.0684 0.0708 AW Gem 0.0730 0.0787 HT Cas 0.0736 0.0761 VW Hyi 0.0743 0.0767 Z Cha 0.0745 0.0773 WX Hyi 0.0748 0.0774 SU UMa 0.0764 0.0788 BR Lup 0.0822 0.0822 TY PsA 0.0840 0.0877 YZ Cnc 0.0868 0.0913 TU Men 0.1180 0.1255 WX Cet (0.0513) 0.0530 LL And (0.0550) (0.0570) CY UMa (0.0571) 0.0593 AL Com 0.0583 (0.0606) CI UMa 0.0604 (0.0628) EK TrA (0.0624) 0.0649 BC UMa 0.0632 (0.0657) UV Per (0.0637) 0.0663 AQ Eri (0.0644) 0.0670 2138-453 0.0646 (0.0672) SS UMi (0.0672) 0.070 RZ Sge (0.0673) 0.0702 EX Hya 0.0682 (0.0711) FO And (0.0700) 0.0730 RZ Leo 0.0708 (0.0739) AY Lyr (0.0728) 0.0760 V503 Cyg 0.0760 (0.0794) CU Vel (0.0765) 0.0799 TT Boo 0.0771 (0.0806) EF Peg (0.0832) 0.0871 KK Tel 0.0840 (0.0880) DM Dra 0.0868 (0.0909) ^1 Numbers in () were calculated using the Eq. in text. The observation of LL And at outburst confirms it as a dwarf nova. The superhumps observed allow us to be fairly confident that LL And has a short orbital period. See Howell and Hurst (1994) for more details. Steve B. HOWELL Planetary Science Institute 620 N. 6th Avenue Tucson, Arizona 85705 USA Guy M. HURST The Astronomer Group 16, Westminster Close Basingstoke, Hampshire RG22 4PP, England References: Howell, S.B. and Hurst, G.M., 1994, J.B.A.A., in press Kato, T., 1993, The Astronomer Electronic Circular, 799 Molnar, L.A. and Kobulnicky, H.A., 1992, ApJ, 392, 678 [BIBCODE 1992ApJ...392..678M ] Nelson, L.A., Chau, W.Y. and Rosenblum, A., 1985, ApJ, 299, 658 [BIBCODE 1985ApJ...299..658N ] Vanmunster, T. and Poyner, G., 1993, The Astronomer Electronic Circular, 795 Wild, P., 1979, IAUC #3412 [BIBCODE 1979IAUC.3412....1W ]