On the stability of the long-term variability of the Double Periodic Variables

Details On the stability of the long-term variability of the Double Periodic Variables On the stability of the long-term variability of the Double Periodic Variables

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006rmxac..26q.173m&link_type=abstract

XI IAU Regional Latin American Meeting of Astronomy (Eds. L. Infante & M. Rubio) Revista Mexicana de Astronomía y Astrofísica (S

Astronomy and Astrophysics

Astronomy

Scientific paper

We have analyzed times of maxima and minima in the long-term light curves of the recently discovered double periodic variables (DPVs, Mennickent et al. 2003, A&A, 399, L47) in order to enlighten the nature of their photometric variability. Whereas it seems well established that the short-term variability is strictly periodic and seems to be well explained as ellipsoidal variations in a close binary system, we find the long-term variability non strictly periodic, with an hitherto unexplained origin.
We have examined OGLE and MACHO light curves of DPVs spanning a time range of 11 years. We measured times for maxima and minima, using the centers of polynomial fits to the peaks. Poorly-resolved peaks were rejected from our analysis. The method was successful for all stars except for the eclipsing systems, where the crowding of the photometric points avoided to find accurate timings. In order to increase the statistical significance of our results, and using the observation that the long-term variability is well represented by a sinusoid (M03), we considered maxima and minima altogether in our analysis. We considered the nth observed peak HJDn and calculated the period P2, by fitting the data with the function HJDn = HJD0 + n(P2/2) . In order to test the stability of the period we constructed O-C diagrams. We find that the systems can be grouped in: G1-type, those systems with brief but significant excursions of timings around the predicted value (7 cases), G2-type, those with short-lived tendencies of increasing or decreasing period (9 cases), G3-type, those with a global pattern of decreasing or increasing period (7 cases) and G4-type, those with random distribution of timings around the predicted value (7 cases).
In a forthcoming paper we will provide an atlas for the long-term variability of double periodic variables.

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