Last revised on August 29, 1997
Department of Physics
Texas A&M University
College Station, TX 77843-4242
Department of Physics and Astronomy
Stephen F. Austin State University
Nacogdoches, TX 75962-3044
A light curve of the Beta Lyrae type eclipsing binary star 68 Herculis is presented, based on 480 photoelectric measurements made at the Texas A&M observatory. Data were collected between October 1995 and July 1996 with U, B, V, R, and I filters. A previously determined period and epoch are confirmed.
The star 68 Herculis (u Herculis, HD 156633, SAO 65913) is a Beta Lyrae type eclipsing binary. It was discovered to be variable by J. Schmidt in 1869, and was found to be an eclipsing binary in 1909 by Baker. The maximum magnitude of the system is about 4.7 and the minima alternate between about 5.0 and 5.4. The primary star is of spectral type B2 and the secondary is B9. Numerous studies have been made of this star in the intervening years, although no thorough sets of data have been collected for 68 Herculis in the past decade. Jabbar (1987) provides a fairly thorough index of other past studies of this star as well as his own.
From October 1995 to July 1996, 480 photometric brightness measurements were made. A 14-inch Schmidt-Cassegrain (f/11) telescope was used along with an Optec SSP-3 solid state photometer and filters closely matching the Johnson U, B, V, R, and I filter system to measure the brightness of 68 Herculis. An Optec SSPCARD (IBM PC Interface Card) was used to collect the data. All measurements were made at the Texas A&M University Observatory located just west of College Station, Texas (30.6deg.N, 96.3deg.W). The comparison star used for all measurements was 59 Herculis. 72 Herculis was used as a check star. 59 Herculis is listed in the literature as a suspected variable, but recent studies (van der Veen, 1984) have indicated it is likely constant in magnitude. We took measurements of 72 Herculis in the V band for use as a check star for 59 Herculis and our measurements do not show evidence of variability. 68 Herculis has a visible 10th magnitude companion 4.5 arcseconds away (Burnham, 1978). However, its contribution to the total light from the system is insignificant (1/100th of the average total intensity).
III. LIGHT CURVES
Figures 1 through 5 show the ultraviolet, blue, visual, red, and infrared light curves (magnitude difference versus orbital phase). For our plots the magnitude difference for any filter [[Delta]]f is the magnitude of the variable star minus the magnitude of the comparison star were f is U, B, V, R, or I. The orbital phases were computed using the ephemeris from Henden and Kaitchuck (1982)
Figure 1: Ultraviolet Filter Light Curve.
Figure 2: Blue Filter Light Curve.
Figure 3: Visual Filter Light Curve.
Figure 4: Red Filter Light Curve.
Figure 5: Infrared Filter Light Curve.
IV. ANALYSIS AND CONCLUSION
A period search was performed on the raw data using Fourier analysis techniques (Belserene, 1988). Discrete Fourier transform of our data indicate a period of about 2.05 days, but more attempts to get a more precise value gave inconsistent results. Plotting our data in accordance with the period and epoch listed by Henden and Kaitchuck (1982) reveals that the period and epoch from Henden and Kaitchuck appears to be valid. Future analysis of the light curves will reveal the relative sizes and shapes of the companions as well as a few orbital parameters of this binary star system.
We would like to thank Richard Schmude and Chris Dahl for their assistance with data collection. The authors would also like to thank the Department of Physics at Texas A&M University for their support of the TAMU Observatory and student projects like this. We are grateful to the Centre de Donnies Astronomiques de Strasbourg for access to the SIMBAD database (http://cdsweb.u-strasbg.fr/). Our data will also be contributed to the AAVSO archives.
Belserene, E. P., Sky & Tel., September 1988.
Burnham, R. 1978, Burnhams Celestial Handbook, Vol. 2, Dover Publications, pp. 952, 970.
Henden, Arne A. and Kaitchuck, Ronald H.1982, Astronomical Photometry, Van Nostrand Reinhold Company.
Jabbar, S.R., Jabir, N.L., and Fleyeh, H.A. 1987, Astrophys. Space Sci., 135, p.377-388.
van der Veen, W.E.C.J. 1984, Astron. Astrophys. Suppl., 57, p.139-153.
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