Spatially resolved optical spectroscopy of the Herbig Ae/Vega-like binary star HD 35187

Abstract

We report on observations of the young binary system HD 35187 (SAO 77144). For the first time, we have obtained spatially resolved optical spectra of the individual stars. Analysis of their effective temperatures indicates that the stars have spectral types of A2 (HD 35187B) and A7 (HD 35187A). Analysis of the Hγ Balmer line indicates a luminosity class V for both stars. At the time of these observations, net Hα emission was present only towards HD 35187B. However, there is evidence that the photospheric Hα line in HD 35187A has been ‘filled in’ relative to its expected strength in an A7 star, so this star may also be associated with some process leading to Hα emission. Moreover, both stars exhibit absorption in the He iλ5876 line well in excess of that expected for their spectral types. Comparison with earlier observations reveals that both the Hα and He i lines are variable, so both stars are ‘active’ in some sense. We suggest that the variable He i absorption detected towards both stars is a result of chromospheric activity, and is not necessarily related to the circumstellar environment. We find tentative evidence for a narrow Ca K circumstellar absorption line and excess redshifted absorption of the Na D line profiles in the spectrum of HD 35187B, both of which are absent in the spectrum of HD 35187A. The heliocentric radial velocity of the presumed circumstellar Ca K line (+54.5 km s−1) is similar to that of redshifted circumstellar absorption lines previously identified in IUE spectra of this star, and the velocity range of the Na D absorption precisely matches that of the UV circumstellar components. Moreover, by placing the stars on the HR diagram (with the aid of the reliable Hipparcos distances) we find evidence that HD 35187B is dimmed by about 0.4 mag of grey circumstellar extinction. The detection of net Hα emission, circumstellar absorption lines, and significant circumstellar extinction for HD 35187B suggests that it has far more mass in its circumstellar environment than its companion, and that the observed IR excess of this system originates from a disc surrounding HD 35187B alone.