δScuti stars in Praesepe

Abstract

Abstract. We present the results of a large international spectroscopic campaign on the δ Scuti star BN Cnc. Combining observations from five observatories taken over more than two weeks, we calculate line indices of the Hα line. A line index is the integrated line flux in a software filter divided by the continuum flux. We demonstrate that this can be used in combination with simultaneous photometry to classify the oscillation modes. We recover all the frequencies also found from photometry and assign likely mode identifications, which differ slightly from previously published values, but are found to be consistent with simple models. The difference in identification is found to have very little effect on the derived luminosity and temperature.

Time-series spectroscopy of pulsating sdB stars -- III.Line indices of PG 1605+072

“…In this way, the line index can be thought of as being similar to the Strömgren Hβ index, calculated using software filters. (For a justification of the term 'line index' as an analogue to a colour index, see Dall et al 2002.) The software for calculating line indices has been collected in a software package called IX, as described by Dall (2000).…”

“…We measure the line index, a quantity that depends on the temperature and surface gravity sensitivity of the equivalent width. It is defined as (Dall et al 2002), where C x is the continuum count level at pixel x , S x is the source count level and W is a Gaussian‐like weighting function for the line in question. The value of C x is found using C x =∑ S x W /∑ W , where W is a broad filter function and is also Gaussian‐like.…”

“… W is centred by moving an integration weight filter across the line in question. The position that maximizes the sum through this filter is taken as the line centre (Dall et al 2002). The width of the function can be chosen arbitrarily; we have chosen the approximate full width at half maximum of each Balmer line, which means we use a different filter for each line.…”

“…In this paper we calculate line indices , which depend on the temperature and surface gravity sensitivity of the equivalent widths of spectral lines. This method has been used to identify modes in the δ Scuti stars FG Vir (Viskum et al 1998) and BN Cnc (Dall et al 2002), and to detect equivalent‐width oscillations in the Hα line of the roAp star α Cir (Baldry et al 1999). Here we present the first detection of line index variations in a pulsating sdB star, namely PG 1605+072, and find a dramatic dependence of line‐index amplitude on the Balmer line number.…”

Delta Scuti stars in the Praesepe cluster observed by the MOST satellite

“…Several variability surveys in the Praesepe cluster have been undertaken (e.g., Breger 1970;Frandsen et al 2001, Dall et al 2002 and have revealed a number of low-amplitude δ Sct stars. The pulsations of these stars are of interest, because as cluster members they share similar properties such as chemical abundance and their distances are accurately known.…”