Time-Series Ensemble Photometry of SX Phoenicis Stars. I. BL Camelopardalis

Abstract

We present an analysis of the multiperiodic SX Phoenicis star BL Camelopardalis (GD 428). Along with 24 times of maximum light from archival data, six previously unpublished times of maximum light from photomultiplier observations and 39 new CCD observations of maximum light are reported. The new CCD observations indicate that BL Cam is a double-mode variable with a primary period of 0.0391 day, a secondary period of 0.0306 day, and a tti/tto ratio of 0.783. The relation between metallicity and period ratio for large-amplitude ô Scuti variables is examined in detail. Finally, evidence is presented that the fundamental period ir 0 has increased by 0.009 s in the last 20 years.

A comprehensive study of the SX Phoenicis star BL Camelopardalis

“…Similar microvariability has been previously found in some other high-amplitude δ Sct and SX Phe-type variables (SX Phe itself and DY Peg by Garrido & Rodríguez 1996; AI Vel by Walraven et al 1992; RV Ari by Pócs et al 2002; RY Lep by Rodríguez et al 2003). In order to investigate microvariability in BL Cam, we have re-analysed the data sets available in the bibliography which are reliable for this task: those of Hintz et al (1997), Kim et al (2003), Wolf et al (2002) and Zhou et al (1999Zhou et al ( , 2001. In addition, our best observation runs were also investigated: those obtained at Xinglong Station (in the period November-December 2003) and Château-Renard Observatory (October 2003).…”

“…However, a puzzling problem in the pulsation analysis comes from the fact that, from time to time, amplitude variations can appear in the form of progressive decreases or increases on the height of the maximum (e.g. at HJD 2 449 750, Hintz et al 1997, Fig. 2; or at HJD 2 452 925, Fig.…”

“…Besides the main pulsation, a secondary periodicity was first identified by Hintz et al (1997). Their photometric data suggested a radial double-mode pulsation nature with a primary ( f 0 ) to secondary ( f 1 = 32.6443 cd −1 ) frequency ratio of f 0 / f 1 = 0.783.…”

“…If confirmed by new observations, BL Cam would have the most complex pulsation spectra among the field highamplitude SX Phe-type variables, and one of the most complex among the general population of SX Phe variables. Hintz et al (1997) were the first to detect a secular increase in BL Cam's primary frequency using the classical O−C method. A more detailed analysis of their O−C diagram, by Breger & Pamyatnykh (1998), revealed a 0.02 s increase over the last 20 years.…”

Period Changes in the SX Phoenicis Star DY Pegasi

“…From each CCD frame, we determined instrumental magnitudes for DY Peg and available comparison stars in the field. We used the methods detailed in Hintz et al (1997) to select a set of comparison stars from those measured. These differential magnitudes and the HJD values were then used to plot the light curves for all nights.…”