A Digital Low Dispersion Spectral Library Covering the 3500-7500AA Region Using the SAAO Radcliffe 1.9m Telescope's Cassegrain Spectrograph

TL;DR

This paper presents a comprehensive digital spectral library of standard stars covering 3500-7500AA, created with the SAAO Radcliffe 1.9m telescope, to aid in stellar classification and cluster membership analysis.

Contribution

The authors developed a new low-resolution optical spectral library for common stellar types, useful for spectral classification, cluster studies, and educational purposes.

Findings

Spectral types for 76 cluster members were derived.

Reddening of NGC 6475 was measured as E(B-V)=0.068.

Spectral data helped identify true cluster members.

Abstract

We have created a digital spectral library, using low resolution optical spectra, of photometric and spectral standard stars. The data were acquired using the Cassegrain Spectrograph installed on the 1.9m Radcliffe telescope at the South African Astronomical Observatory. The library consists of optical wavelength (~ 3500-7500AA) spectra for main sequence and giant stars encompassing those most commonly observed in the Galaxy, namely the late-B, A-, F-, G-, K-, and early- to mid-M stars. We intend that our standard star spectra will be especially useful for spectral classification of stars in the field and Galactic clusters alike, and will have high pedagogic value when included into representative Introductory Astronomy or Stellar Astronomy curricula for undergraduate astronomy major and minor programs. We exploit the spectral library in order to derive spectral types for seventy-six optically and X-ray selected members of the young open cluster NGC 6475. Comparison of spectral-type, optical and infrared photometric data to theoretical colors derived from spectral type show that the reddening of the cluster is E(B-V) = 0.068 +/- 0.012 (1sigma=0.058), a vector consistent with earlier surveys. Our analysis also highlights the utility of such spectra in rejecting cluster non-members, thereby allowing the creation of a clean sample of bona fide cluster members for follow-up science observations.