Survey confirms 81 new variable stars

As a member of the AAVSO, variable star astronomy is near and dear to my heart. Astronomers at the Moletai Astronomical Observatory (MAO) in Lithuania recently submitted their results on the photometric variability analysis of 3,598 stars in the northern sky that revealed 81 new variable candidates. The authors state that the mission of MAO is

to deliver a full spectroscopic characterisation and variability information of the brightest stars in the northern sky.

Why would this be of importance? Well, one very significant reason would be to inform exoplanet searches such as NASA's Transiting Exoplanet Survey Satellite (TESS) and ESO's PLAnetary Transits and Oscillations (PLATO).

To this end, the astronomers used a 51 cm telescope with an Apogee CCD camera. This combination afforded the researchers a wide field of view (37.5 x 37.5 arcmin) and allowed for observation of bright stars without saturation. The survey covered about 5.85 square degrees of the sky and was subdivided into 13 fields. Each night 5 - 7 fields were observed. Naturally, the exposure time for each field varied depending on the brightness of the objects being observed. However, but the observing cadence produced between 9 - 15 images for each survey field every 15 - 30 minutes. The overall results are shown in Figure 1 below.

Figure 1. Top panel shows a histogram of the magnitudes of the survey. Middle panels shows a histogram of the mean errors. Bottom panel shows a histogram of the standard deviation. Credit: Pakstiene et al. 2019

As you can see above in Figure 1's top panel, the magnitudes of the survey stars ranged from about 8th magnitude (brightest) to 16th magnitude (dimmest) with an average somewhere between 14-15 magnitude. The middle panel shows the average error the observation which is impacted by things like conditions in the atmosphere (e.g., weather). The bottom panel shows a histogram for the standard deviations. This is important for finding variables because researchers are looking at stars with higher standard deviations as potential variable stars (i.e., their magnitude is not constant so their standard deviation is larger).

Of the 3,598 stars imaged in the survey, 81 were identified as new (or newly confirmed) candidate variables. Each individual star was analyzed using special programs that search for periodicity in the data (e.g., Lombscargle). If a strong enough signal was found in the data, a light curve was constructed to see if the results made sense. For example, one particularly interesting finding was a newly confirmed eclipsing binary (TYC 2764-1997-1) and its light curve is shown below in Figure 2.

Figure 2. Phase folded light curve of eclipsing binary TYC 2764-1997-1 with a period of 7.8028 hours. Credit: Pakstiene et al. 2019

TYC 2764-1997 had previously been listed in the SIMBAD database as an unconfirmed eclipsing binary with a period of 7.8012 hours. The newly calculated period of 7.8028 hours is slightly longer suggesting that there may have been a loss of angular momentum due to mass transfer between the objects. These type of followup studies will continue to be invaluable not only to refine our understanding of each star system, but to inform future research in areas such as exoplanet searches.

References

Pakstiene, E. et al., 2019, https://arxiv.org/pdf/1902.06357.pdf