A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL Α CYGNI VARIABLE AND a-Type SUPERGIANT STAR DENEB

Abstract

Deneb is often considered the prototypical A-type supergiant, and is one of the visually most luminous stars in the Galaxy. A-type supergiants are potential extragalactic distance indicators, but the variability of these stars needs to be better characterized before this technique can be considered reliable. We analyzed 339 high resolution echelle spectra of Deneb obtained over the five-year span of 1997 through 2001 as well as 370 Strömgren photometric measurements obtained during the same time frame. Our spectroscopic analysis included dynamical spectra of the Hα profile, Hα equivalent widths, and radial velocities measured from Si II λλ 6347, 6371. Time-series analysis reveals no obvious cyclic behavior that proceeds through multiple observing seasons, although we found a suspected 40 day period in two, non-consecutive observing seasons. Some correlations are found between photometric and radial velocity data sets, and suggest radial pulsations at two epochs. No correlation is found between the variability of the Hα profiles and that of the radial velocities or the photometry. Lucy (1976) found evidence that Deneb was a long period single-lined spectroscopic binary star, but our data set shows no evidence for radial velocity variations caused by a binary companion.

Evolution of blue supergiants and α Cygni variables: puzzling CNO surface abundances

“…The other two periods are in the longer part of the observed range. The periods of excited radial modes are much longer than the periods of radial pulsations, 17.8 and 13.4 days, obtained by Richardson et al (2011). The reason for the discrepancy is not clear.…”

“…Deneb is the prototype of the α Cygni variables and has a long history of studies (see Richardson et al 2011, for a review and references given). Although its light-curves are very complex, Richardson et al (2011) obtained radial pulsation features at two short epochs. Strangely, however, the two epochs give two different periods; 17.8 days and 13.4 days.…”

“…Strangely, however, the two epochs give two different periods; 17.8 days and 13.4 days. From the time-series analyses by Richardson et al (2011) and Kaufer et al (1996), we have adopted a period range of 10 − 60 days. On the HR diagram Deneb is close to the blue-loop of Mi = 25 M⊙ (Fig.…”

ASTEROSEISMOLOGY OF THE NEARBY SN-II PROGENITOR: RIGEL. I. THEMOSTHIGH-PRECISION PHOTOMETRY AND RADIAL VELOCITY MONITORING

“…Fascinating features of BSGs include their microvariability in flux (e.g., Sterken 1977), complex changes in radial velocity (RV), as well as variations in the equivalent widths (EW) and line profiles of Balmer (especially Hα) and metallic lines (Kaufer et al 1996(Kaufer et al , 1997Richardson et al 2011). Kaufer and coworkers monitored the optical spectra of six BA supergiants (including Rigel and α Cyg).…”

Spectral atlas of A-type supergiants

“…Absolute M V magnitudes for α Cyg, 3 Pup, and BD +48 • 1220 from [16], [14], and [13] respectively, are given in the third column. The last two columns show the mid-exposure time in JD and the heliocentric radial velocity V r measured by numerous (n > 500) symmetric absorptions and its variability are presented by Richardson et al [17], who carried out a long-term spectral monitoring with a high spectral resolution in combination with Strömgren system photometry. However, despite the long-term observations of α Cyg, the nature of its variability remains unclear as long as the estimates of the star's mass and its brightness variability periods are not definitely stated [17,18].…”