Spectral classification of the cool giants in symbiotic systems

Abstract

Abstract. We derive the spectral types of the cool giants in about 100 symbiotic systems. Our classification is mainly based on near IR spectra in order to avoid the contamination of the spectrum by the nebula and the hot component in the visual region. The accuracy of our spectral types is approximately one spectral subclass, similar to previous near IR classification work, and much better than visual spectral type estimates.Strong, intrinsic spectral type variations (> 2 spectral subtypes) are only seen in systems containing pulsating mira variables.We present a catalogue of spectral types for cool giants in symbiotic systems which also includes determinations taken from the literature. The catalogue gives spectral types for the cool giants in about 170 systems which is nearly the full set of confirmed symbiotics.Based on our classifications we discuss the distribution of spectral types of the cool giants in galactic symbiotic binaries. We find that the spectral types cluster strongly between M3 and M6, with a peak at M5. The distribution of systems with a mira variable component peaks even later, at spectral types M6 and M7. This is a strong bias towards late spectral types when compared to red giants in the solar neighbourhood. Also the frequency of mira variables is much larger among symbiotic giants. This predominance of very late M-giants in symbiotic systems seems to indicate that large mass loss is a key ingredient for triggering symbiotic activity on a white dwarf companion.Further we find for symbiotic systems a strong correlation between the spectral type of the cool giant and the orbital period. In particular we find a tight relation for the minimum orbital period for symbiotic systems with Based on observations obtained with the 1.52 m and 3.6 m telescopes of the European Southern Observatory (ESO), the 1.93 m telescope of the Observatoire de Haute-Provence (OHP), the 2.3 m telescope of the Australian National University (ANU) at Siding Spring, and the William Herschel Telescope (WHT) at La Palma. This research has made use of the AFOEV database, operated at CDS, France. red giants of a given spectral type. This limiting line in the spectral type -orbital period diagram seems to be equivalent with the relation R ≤ 1 /2, where R is the radius of the red giant and 1 the distance from the center of the giant to the inner Lagrangian point L 1 . This correlation possibly discloses that symbiotic stars are -with probably only one exception in our sample -well detached binary systems.

Spectroscopic binaries among Hipparcos M giants

“…They correspond to Roche lobefilling factors R/R R , which are much too small for circularisation to operate efficiently (i.e., on a time scale comparable to the RGB evolutionary time scale). Interestingly enough, a similar difficulty has been pointed out by Mürset & Schmid (1999) and Mikołajewska (2007) in the context of symbiotic stars. a This number differs from the one quoted by Famaey et al (2005), because we restrict the sample to stars having at least two radial-velocity measurements; b at the level Prob(χ 2 (Vr)) ≤ 0.001.…”

The Henize sample of S stars

“…All detailed abundance studies performed so far for yellow symbiotics have revealed heavy-element overabundances resembling those observed in S stars (Schmid 1994;Smith et al 1996Smith et al , 1997Pereira & Porto de Mello 1997;Pereira et al 1998;Smith et al 2001;Pereira et al 2003). On the contrary, not a single red symbiotic star from the catalogue of Mürset & Schmid (1999) seems to exhibit the ZrO distinctive spectral features of S-type stars. This puzzling situation is reviewed by .…”

Orbital eccentricity of the symbiotic star MWC 560

“…Mürset & Schmid (1999) give M5.5III -M6III as its stellar type. According to van Belle et al (1999), a typical M5III giant has the following parameters:…”