The EC 14026 stars - VII. PG 1605 + 072, a star with many pulsation modes

Abstract

We report the discovery of large-amplitude ( -0.25 mag) pulsations in the bright (V= 12.8) sdB star, PG 1605 + 072. The dominant period is 480 s, but more than 20 periods were present on at least three separate occasions. Frequency analysis of the complete data set yields more than 30 periods. A few of these are harmonics or linear combinations of the strongest modes. Excluding the latter, the periods span a range of almost 400 s, which contrasts with the typical range < 20 s for most other EC 14026 stars.Analysis of multicolour photometry limited any cool companion to being a mainsequence star of type MO or later. Balmer line profile fitting yielded an effective temperature of 32 100 + 1000 K and a log g of 5.25 + 0.10, significantly smaller than in the other stars of the EC 14026 class, and possibly indicative of a more evolved state. The lower gravity is probably responsible for the fact that the pulsation periods and amplitudes are respectively much longer and larger than in other stars of the class. This star is an obvious target for asteroseismological investigation using a multilongitude photometric campaign.

Time-resolved spectroscopy of the sdBV V338 Serpentis

“…When f 1 and f 2 are in the constructive phase of their beat cycle, they again beat with f 1 on a 27 µHz cycle, or 0.42 days, which corresponds to the beat pattern seen in the Mercator observations. Thus, an interpretation based on the Kilkenny et al (1999) frequencies is perfectly consistent with the behaviour we see in our photometric data, with the only exception that all the main frequencies have more than twice the amplitude of what was observed in the 1997 campaign, and much closer to the amplitudes observed by Koen et al (1998). This amplitude difference is even more substantial for the first harmonic of the main mode, which was observed at the millimagnitude level (f 24 in Kilkenny et al 1999) while we observe it at an amplitude close to 6.8 mma, again in agreement with Koen et al (1998).…”

“…V338 Ser (PG 1605+072) is one of only five known sdBV stars brighter than V = 13.0, and was one of the first 10 sdBVs discovered by the South African group and published in the initial rush of papers in 1997-98 (Koen et al 1998). It was recognised early to be a spectacular pulsator in that it has the highest pulsation amplitude observed in any sdBV R star, and a quite complex pulsation pattern indicating several modes of considerable amplitude.…”

Multicolour photometry of Balloon 090100001: linking the two classes of pulsating hot subdwarfs

“…The semi‐amplitudes in all filters are given in Table 1. It is worth noting that, along with the main mode in V338 Ser (Koen et al 1998a), the f 1 mode has the largest amplitude of all modes known in EC 14026 stars. Generally, the semi‐amplitudes become smaller towards longer wavelengths as the theory predicts (see, e.g.…”

Adiabatic Survey of Subdwarf B Star Oscillations. II. Effects of Model Parameters on Pulsation Modes

“…There are currently 19 sdB pulsators (now referred to as the EC 14026 stars after the prototype) known in the public domain (O'Donoghue et al 1999;Billères et al 2000;Silvotti et al 2000;Brassard et al 2001;Ostensen et al 2001). Most of them are found around log g ' 5:8 and T eff ' 34;000 K, but there are known outliers such as Feige 48 at log g ' 5:4 and T eff ' 29;000 K (Koen et al 1998c), HS 2201+2610 at log g ' 5:4 and T eff ' 29;300 K (Ostensen et al 2001), and PG 1605+072 at log g ' 5:2 and T eff ' 31; 000 K (Koen et al 1998b). The EC 14026 stars are all multiperiodic variables with typical periods in the range 100-200 s and typical amplitudes of several millimagnitudes.…”