Hot star extension to the Hubble Space Telescope stellar spectral library^★

Department of Physics and Astronomy, Washington State University, Pullman, WA, USA
e-mail: islam.khan@wsu.edu; gworthey@wsu.edu

Received: 23 December 2017
Accepted: 21 March 2018

Abstract

Context. Libraries of stellar spectra find many uses in astrophysics, from photometric calibration to stellar population synthesis.

Aims. We present low resolution spectra of 40 stars from 0.2 μm (ultraviolet) to 1.0 μm (near infrared) with excellent fluxing. The stars include normal O-type stars, helium-burning stars, and post-asymptotic giant branch (PAGB) stars.

Methods. Spectra were obtained with the Space Telescope Imaging Spectrograph (STIS) installed in the Hubble Space Telescope (HST) using three low resolution gratings, G230LB, G430L, and G750L. Cosmic ray hits and fringing in the red were corrected. A correction for scattered light was applied, significant only for our coolest stars. Cross-correlation was used to bring the spectra to a common, final, zero velocity wavelength scale. Finally, synthetic stellar spectra were used to estimate line of sight dust extinction to each star, and a five-parameter dust extinction model was fit, or a one-parameter fit in the case of low extinction.

Results. These spectra dovetail with the similar Next Generation Stellar Library (NGSL) spectra, extending the NGSL’s coverage of stellar parameters, and extending to helium burning stars and stars that do not fuse.

Conclusions. The fitted dust extinction model showed considerable variation from star to star, indicating variations in dust properties for different lines of sight. Interstellar absorption lines are present in most stars, notably Mg II.