Time-resolved spectroscopy of the bright sdBV Balloon 090100001

Abstract

We have obtained 2552 useful low-resolution spectra of the bright sdBV Balloon 090100001, which form the first large time-resolved spectroscopic dataset of this brightest known pulsating subdwarf B star. The data were obtained at the Nordic Optical Telescope during 7 nights in August/September 2004 over a total time base of 38 nights, aiming to derive pulsational characteristics of this star. In this paper we present the observations and the results obtained from frequency analyses. In our data we find clear evidence for 8 independent frequencies, that were all previously reported in photometric monitoring studies, allowing future asteroseismological studies of this star to be constrained by combined photometric and spectroscopic observations of as much as 8 pulsation modes. We do not find conclusive evidence for new frequencies. We present the first determination of the pulsational radial-velocity amplitudes of this star, and find that the radial-velocity amplitude of the main pulsation mode ( f 1 = 2.80749 mHz) in Balloon 090100001 is 18.9 km s −1 , which is the largest radial-velocity amplitude found in sdB-star pulsations so far. For all spectra, the radial velocities are published electronically.

Asteroseismology and evolution of EHB stars

“…The exceptional amplitude of the dominant period in BA09 has hinted towards a radial nature, and this was finally confirmed by Baran et al (2008) by combining evidence from multicolor photometry and the radial velocity amplitude measured by Telting & Østensen (2006). Van Grootel et al (2008) have successfully applied the forward method to BA09, demonstrating some peculiarities in the model predictions.…”

Interpreting the line-profile variations of subdwarf B pulsators: the case of PG 1336-018 (NY Virginis)

“…The first time-resolved spectroscopy study was done by Jeffery & Pollacco (2000) on PB 8783 and KPD 1929+4401, followed by extensive studies on PG 1605+072 by Woolf et al (2002), O'Toole et al (2000O'Toole et al ( , 2002O'Toole et al ( , 2003aO'Toole et al ( , 2005 and Tillich et al (2007), on PG 1325+101 by Telting & Østensen (2004), on Balloon 090100001 by Telting & Østensen (2006) and Østensen et al (2008) and most recently on PG 1219+534 by Reed et al (2009). These low-resolution spectroscopy studies were mainly focused on measuring the RV and equivalent width variations, as well as characterization of the pulsational effective temperature and gravity variations.…”

“…This is the first application of a line-profile variation study on a V361 Hya star with low photometric amplitudes (<8 mmag), no dominant frequency and a dense and narrow frequency spectrum (28 frequencies were found in a 5000 μHz range, see Table 4 of Kilkenny et al 2003). All previous time-series spectroscopy studies, including the recent line-profile analysis by Telting et al (2008), were done on V361 Hya outliers with exceptionally high amplitudes (O'Toole et al 2000(O'Toole et al , 2002(O'Toole et al , 2003a(O'Toole et al , 2005Woolf et al 2002;Telting & Østensen 2004Telting & Østensen , 2006Tillich et al 2007). …”

Testing the forward modeling approach in asteroseismology

“…For these reasons, BAL 0901 has been observed and studied extensively over the recent past, including, for example, UBVR photometry reported by Baran et al (2005) and analyzed by Tremblay et al (2006), and time-resolved spectroscopy carried out at the Nordic Optical Telescope in August/September 2004 (Telting & Østensen 2006). Notably, Baran et al (2008) recently reused these two sets of observations that were coincidentally obtained at the same time and proposed -identifications for the five dominant modes based on a combined analysis of the multicolor photometry and the spectroscopy.…”