SHON - Article

New Probably Variable in Monoceros - GSC 4837.0908

Petr Molik

Petrin Hill Observatory, Strahovska 205, 118 46 Prague 1, Czech Republic

On the night of November 21/22, 1994, I was making visual observations of the eclipsing binary IL Mon with the use of 20 cm (8 in.) refractor at the Petrin Hill Observatory in Prague (Czech Republic). Focal length of this instrument was 137 cm (4,5 ft), magnification 137 times. Visual estimates were done by the method of Nijland-Blazhko. At 2:16 UT I noticed that the star GSC 4837.2146, which I had chosen several weeks earlier as the brightest comparison star ("A"), is apparently fainter than GSC 4837.0908 (comparison star "B"). About two hours later, at 4:32 UT, the comparison star "A" remained fainter than "B". This led me to a suggestion that one of these stars might be variable. Because the General Catalogue of Variable Stars, the New Catalogue of Suspected Variable Stars, and the more recent Name-Lists of Variable Stars do not contain any variable in the positions of the stars "A" and "B" it was necessary to prove or disprove their variability by further observation.

Within the following four months I observed these stars visually in 14 nights. During most of the nights the star "A" remained fainter than "B" and both the stars did not show any change of brightness. However, on the nights of December 11/12, January 4/5, and March 6/7 the relative brightness of these stars was gradually changing and the comparison star "A" was for several hours brighter than "B". The observations seemed to confirm the variability of one of these stars but it still was not clear to me which of the two stars was variable. The difficulty consisted in the fact that in given field there was no other star suitable for comparison (other stars were either too bright or too faint). Only on March 23, 1995, after processing all my observational data (about 150 visual estimates of brightness obtained from December, 1994 to March, 1995), I concluded that the star "A" is non-variable and that a new variable is the star "B" (GSC 4837.0908). The new variable is probably an eclipsing binary with orbital period of about 12 days and amplitude of about 0.5 mag in visual light. The duration of eclipses (D) is approximately 10 hours.

Dr. M. Wolf of the Astronomical Institute, Charles University, Prague, monitored the field containing the above mentioned stars with a CCD camera (SBIG ST-7) attached to the 0.65 m telescope at Ondrejov Observatory during the night of December 17/18, 1994. According to his measurements, the comparison stars "A" and "B" had constant light intensity and "B" was by 0.29 ± 0.02 mag brighter than "A" which corresponded to the maximum brightness of "B". By chance, the photographic plate used as the source of data for the same field in the GSC was exposed just at the time of minimum light of the star "B" so the GSC magnitudes are 10.95 ± 0.40 mag and 11.36 ± 0.40 mag for "A" and "B", respectively. The CCD differential magnitude as well as the GSC photographic magnitudes are close to standard V magnitudes. They can be considered as an objective confirmation of the variability of the star "B".

Table 1 lists four times of minimum light of the new variable. The Julian dates are given to four decimals for formal reasons only. The real accuracy of the minimum timings is not better than ± 10 minutes.

Table 1: Times of minimum light of GSC 4837.0908.

Preliminary light elements of the new variable are the following:

In Figure 1 it is given a finding chart for the new variable.

Figure 1: Numbers 1-4 indicate the following objects: 1 - comparison star "A" (GSC 4837.2146), 2 - new variable (comparison star "B", GSC 4837.0908), 3 - eclipsing binary IL Mon, 4 - NSV 3811.

Acknowledgements: I am grateful to Dr. Marek Wolf (Astronomical Institute of the Charles University, Prague) for his effort to confirm the variability of GSC 4837.0908 and for printing the chart from the MegaStar Catalogue. I would also like to thank Mr. Jan Manek of the Petrin Hill Observatory in Prague for providing me the data from the Guide Star Catalogue.

References:

Kholopov P. N. et al., 1985-1987: General Catalogue of Variable Stars, 4th ed., Nauka, Moscow

Kukarkin B. V. et al, 1982: New Catalogue of Suspected Variable Stars, Nauka, Moscow

Kholopov P. N., Samus N. N., Kazarovets E. V., Perova N. B., 1985: The 67th Name-List of Variable Stars. Inform. Bul. Var. Stars, No. 2681

Kholopov P. N., Samus N. N., Kazarovets E. V., Kireeva N. N., 1987: The 68th Name-List of Variable Stars. Inform. Bul. Var. Stars, No. 3058

Kholopov P. N., Samus N. N., Kazarovets E. V., Frolov M. S., Kireeva N. N., 1989: The 69th Name-List of Variable Stars. Inform. Bul. Var. Stars, No. 3323

Kazarovets E. V., Samus N. N., 1990: The 70th Name-List of Variable Stars. Inform. Bul. Var. Stars, No. 3530

Kazarovets E. V., Samus N. N., Goranskij V. P., 1993: The 71th Name-List of Variable Stars. Inform. Bul. Var. Stars, No. 3840

Kazarovets E. V., Samus N. N., 1994: The 72th Name-List of Variable Stars. Inform. Bul. Var. Stars, No. 4140

The Guide Star Catalogue, Space Telescope Science Institute, Baltimore, Maryland, U.S.A., V 1.1, 1992, on CD ROM

Additional note made by the author in the year 2007

Photometric data from the sky survey project ASAS-3 (G. Pojmanski, 2003, Acta Astron., 53, 341) do not show any variability of the star GSC 4837.0908 with the period of 12.1124 days given in this paper.

This page hosted by   Get your own Free Home Page