A&A 526, A116 (2011) Astronomy DOI: 10.1051/0004-6361/201015912 & c ESO 2011 Astrophysics Neutral and ionized emission lines in the type II Cepheid W Virginis, V. V. Kovtyukh,1 G. Wallerstein,2 S. M. Andrievsky,1 D. Gillet,3 A. B. Fokin,4 M. Templeton5 A. A. Henden5 1 Astronomical Observatory, Odessa National University, T.G. Shevchenko Park, 65014 Odessa, Ukraine e-mail: [email protected] 2 Department of Astronomy, University of Washington, Seattle, WA 98195, USA e-mail: [email protected] 3 Observatoire de Haute-Provence, 04870 Saint-Michel Observatoire, France 4 Institute for Astronomy of the Russian Academy o Sciences, Moscow, Russia 5 American Association of Variable star Observers, 49 Bay state road Cambridge, MA 02138, USA Received 12 October 2010 / Accepted 7 December 2010 ABSTRACT Aims. The aim of this work was to perform a multiphase spectroscopic study of W Vir which represents stars of the class of population II Cepheids, in order to trace the behaviour of emission features in different lines, and to use the data to describe the dynamical processes in the atmosphere of this star associated with the shock wave propagation. Methods. Our spectroscopic study of W Vir involved 18 high-resolution spectra obtained with the help of 3.5-m telescope of Apache Point Observatory. These spectra cover W Vir’s pulsational cycle with good phase resolution that enabled us to precisely fix the intervals of appearance, existence and disappearance of many anomalous spectral features, as well as to construct their radial velocity curves. Results. We detected and investigated the behaviour of emission and line doubling in many metallic lines (Na I, Fe I, Fe II, Ba II etc), as well as in hydrogen and helium lines. Analysis of the temporal characteristics of those emission features allowed us to make, in particular, the following conclusion. Conclusions. W Vir consists of two parts: the inner part, which is, in fact, a pulsating star itself with periodic shocks penetrating into the upper atmosphere, an outer one – a circumstellar envelope. The interaction of the main shock wave with the infalling envelope layers can explain the observed peculiarities of the spectral line variability. Key words. stars: atmospheres – stars: variables: Cepheids 1. Introduction The shock models was further developed by Whitney & ff Scalafuris (1963). New observation with the Palomar coude In 1938 Joy recognized the di erences between W Vir and the spectrograph by Raga & Wallerstein (1989) served to derive the classical Cepheids he was surveying. High resolution spectra of ratio of H/He in W Vir atmosphere. A further evaluation and im- W Vir were first obtained by Sanford (1953), in which doubled provement in the shock model by Lébre & Gillet (1992)made absorption lines and hydrogen emission lines with inverse P- use of the new high resolution spectra over the whole cycle. Cygni profiles were present from the near minimum light until In this paper we call attention to the numerous emission lines about phase 0.1 past light maximum. of Fe I and other species and trace their appearances and radial These kind of profiles indicate that a shock-wave is pass- velocities. We discuss very briefly the origin of the neutral emis- ing through the atmosphere during rising light. This interpreta- sion lines but do not attempt to derive a principally new model tion had originally been suggested by Schwarzschild (1953)asa for the star’s pulsation. This follows the advice of Walter Baade comment at the 1952 IAU Meeting after Sanford’s presentation to G.W. when he was considering the type II Cepheids for a the- of the spectra of W Vir with double absorption lines and H emis- sis topic: “Just get the kinematics straight. Don’t worry about the sion lines, and the first quantitative model has been developed spectroscopic nonsense”. by Whitney (1956a,b) as reported by Wallerstein (1959). Surprisingly, the emission lines of He I on Sanford’s plates were overlooked by Sanford and others until rediscovered by 2. Observations Wallerstein (1959). The He I emission lines served to confirm the shock model since they indicated that the high temperature As a part of a program to derive the chemical composition of behind the shock was sufficient to ionize He once, as well as H. certain type II Cepheids and RR Lyrae stars, we have obtained spectra of W Vir with the echelle spectrograph of the 3.5-m tele- Based on spectra collected at the Apache Point Observatory, which scope at the Apache Point Observatory. These spectra have a is managed by The Astrophysical Research Consortium. resolving power of about 35 000 and cover the full wavelength Table A.1 (Appendix) and original spectra are only available in electronic form at the CDS via anonymous ftp to from 3500 Å to 10 400 Å though with rather low S/N below cdsarc.u-strasbg.fr (130.79.128.5) or via 3900 Å and above 8800 Å. The uncertainty in the determination http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/526/A116 of velocities is a few tenths of km s−1. This value is typical for Article published by EDP Sciences A116, page 1 of 9 A&A 526, A116 (2011) 3.5 3.5 Table 1. Observations. 3 Hα φ=0.666 3.0 φ=0.006 3.0 φ=0.270 2.5 2.5 2 2.0 2.0 + φ Sp. Date JD 2450000 1.5 1.5 ∗ 1.0 1.0 1 2002.02.22 2328.776 0.201 Flux Relative 1 2 2002.03.02 2336.802 0.666∗ 0.5 0.5 0 0.0 0.0 6555 6560 6565 6570 6560 6565 6555 6560 6565 657 3 2006.01.20 3757.039 0.865 1.3 1.3 4 2006.01.21 3758.041 0.924 1.2 Pashen 1.2 1.2 5 2006.01.22 3759.022 0.981 1.1 1.1 1.0 1.0 1.0 6 2006.01.23 3760.039 0.041 0.9 0.9 7 2006.01.24 3761.033 0.099 0.8 0.8 0.8 0.7 0.7 8 2006.01.27 3764.013 0.270 Flux Relative 0.6 0.6 0.6 9 2006.01.28 3765.032 0.330 8740 8745 8750 8755 8740 8745 8750 8755 8740 8745 8750 8755 10 2006.01.28 3765.041 0.330 1.2 Fe I 11 2006.03.21 3816.756 0.319 0.8 12 2006.06.06 3893.659 0.777 13 2006.06.07 3894.679 0.835 0.4 14 2006.06.08 3895.660 0.893 Flux Relative 15 2006.06.10 3897.617 0.006 6390 6395 6400 6390 6395 6400 6390 6395 6400 1.2 16 2006.06.11 3898.608 0.064 Fe II 17 2006.06.12 3899.668 0.124 0.8 18 2006.06.13 3900.618 0.180 0.4 Relative Flux Relative (∗) Notes. – Phases are calculated using P = 17.2768 d (McSaveney et al. 6430 6435 6440 6430 6435 6440 6430 6435 6440 2005)andJD0= 53742 (Templeton & Henden 2007). Lambda, A Lambda, A Lamda, A Fig. 1. Emissions in different lines. a resolving power of 35 000 and a signal-to-noise ratio greater than 50. On a spectrum obtained on March 2002 ( = JD 2452336.802) the gas above the shock wave front. Helium emission lines were = we have found emission lines of neutral metals. Further spectra detected by Lébre & Gillet between φ 0.83 and 0.01. were obtained in a concentrated campaign during the succeeding months to explore the presence of these lines over a significant part of the star’s 17 day cycle. The spectra were reduced by stan- 4. Emission features in spectra of W Vir dard methods in IRAF and measured with the computer package On 2002 March 3, emission lines of neutral iron were seen. DECH20 (Galazutdinov, priv. comm.). Despite all the spectra of W Vir that have been taken over the We alerted the AAVSO to the need for a simultaneous light past 70 years, emission by neutral metals has been reported only curve to properly phase our spectroscopic observations. In Table by Lébre & Gillet (1992), and only in one Ni I 5893 line (phases 1 we list photometric phases reported by Templeton & Henden 0.74 and 0.83). This was probably due to the fact that for the (2007) that correspond to our spectroscopic observations. It is bright stars the observations with photographic plates were com- very important to note that according to Abt (1954) individual mon in the past, but little work has been done with CCD’s since cycles of W Vir sometimes show phase jitter by 0.1. Thus, a very they were introduced only in the 1980’s. precise phase fix of spectroscopic observations must be obtained Upon careful inspection we found that many emission lines for the specific cycle that was covered. from neutral and ionized species are present. In Table A.1 of the appendix we list the lines of species seen in emission at phase 0.666. Almost all lines present are from neutral atoms with the 3. Results of previous detailed spectroscopic exception of lines of Fe II and some easily ionized species. The studies of W Vir line intensities are related to the continuum by their equivalent The most comprehensive spectroscopic study of W Vir that cov- widths in mÅ units. We have no calibration of the continuum ered a whole pulsation cycle with high time resolution has been flux as a function of wavelength.