Spectroscopy and Linear Spectropolarimetry of the early Herbig Be Stars PDS 27 and PDS 37

Abstract

The number of well-studied early-type pre-main-sequence objects is very limited, hampering the study of massive star formation from an observational point of view. Here, we present the results of VLT/FORS2 spectropolarimetric and VLT/X-shooter spectroscopic observations of two recently recognised candidate Herbig Be stars, PDS 27 and PDS 37. Through analysis of spectral lines and photometry, we find that these two objects are hot, 17500 $\pm$ 3500~K, have large radii, 17.0 $\pm$ 4.0 and 25.8 $\pm$ 5.0~${\mathrm{R}}_{\odot }$, and are very massive, 15.3 (+5.4, -4.4) and 21.1 (+11.0, -5.3)~M${}_{\odot }$ for PDS 27 and PDS 37, respectively. This suggests that these two objects are very young in their evolution and may become O-type stars. Their youth is supported by their high accretion rates of the order of $10^{-3}$--$10^{-4.5}{\mathrm{M}}_{\odot }$/yr. A change in linear polarisation across the absorption component of H$\alpha$ is detected in both objects. This change indicates that the circumstellar environment close to the star, at scales of several stellar radii, has a flattened structure, which we identify as an inner accretion disk. Strong variability is seen in both objects in many lines as further indication of an active circumstellar environment.

15 pages, 9 figures

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Cited by in corpus (8)

• Gaia DR2 study of Herbig Ae/Be stars
• The Polstar High Resolution Spectropolarimetry MIDEX Mission
• Linear spectropolarimetry across the optical spectrum of Herbig Ae/Be stars
• Resolving the MYSO binaries PDS 27 and PDS 37 with VLTI/PIONIER
• Census of High- and Medium-mass Protostars V. CO Abundance and the Galactic $X_{\text{CO}}$ Factor
• Herschel observations of the circumstellar environment of the two Herbig Be stars R Mon and PDS27
• Identification and spectroscopic characterization of 128 new Herbig stars
• Disentangling the two sub-populations of early Herbig Be stars using VLT/X-Shooter spectra