Spectral Observations of Emission Stars in the Vicinity of Cyg OB7
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SPECTRAL OBSERVATIONS OF EMISSION STARS IN THE VICINITY OF Cyg OB7
N. D. Melikian
Results from spectral observations of known emission stars in the vicinity of Cyg OB7 are presented. 64 spectra of 9 emission stars were obtained over the period 2001-2007. The equivalent widths of the most characteristic lines for T-Tau stars were obtained in all these spectra. It is noted that all the spectral lines manifest strong variations. The spectra of these stars are in the spectral range K8-M4. Two stars (Nos. 12 and 23) have a negative Balmer jump. The forbidden [OIII] 4959 and 5007 Å and [SII] 6716/31 Å lines, which are typical of classical T-Tau stars, show up in the spectra of stars No. 23 and 86. Keywords: emission stars: T Tau stars: Cyg OB7
1. Introduction
The discovery of stellar associations was important for research on stellar evolution since the solution of many problems of stellar cosmology is closely related to the discovery and study of these physically unstable systems [1,2]. The discovery and study of T associations by HD surveys are very effective. We began surveys of this kind back in 1979 on the 40" Schmidt telescope at the Byurakan Observatory with a 4° objective prism. The observations were made in several fields of Cepheus and Cygnus, where more than 200 new HD stars were discovered [3-9]. In addition to the HD emission stars, a preliminary analysis of our first observations led to the discovery of the first flare stars
V. A. Ambartsumyan Byurakan Astrophysical Observatory, Armenia; e-mail: [email protected]
Original article submitted May 29, 2020; accepted for publication August 26, 2020. Translated from Astrofizika, Vol. 63, No. 4, pp. 597-609 (November 2020) 0571-7256/19/6304-0523 ©2020 Springer Science+Business Media, LLC
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in these regions [3,4], which are closely associated with T-Tau type stars [10]. The observations begun in 2000 on the 2.6-m telescope at the Byurakan Observatory in the region of Cyg OB7 have been especially fruitful [11-20]. Studies of this region have made it possible to detect a number of interesting objects. Within just a small segment of size 14' × 14', 11 new HD stars have been discovered, of which one manifested flare activity [18], two cometary nebulae associated with emission stars, and three groups of HH objects. The formation of a new nebular object has been detected in the near infrared [11]. Photometric studies of stars in this region have revealed irregular brightness variations of 42 stars in the region, in particular for stars with HD emission [20]. Spectra of 9 of the emission stars were obtained during the period 2001-2007. This paper is devoted to a study of the spectral characteristics of these stars.
2. Observations
In this paper we present results from spectral observations made on the 2.6-m telescope at the V. A. Ambartsumyan Byurakan Observatory during 2000-2005 using the ByuFOSC-2 [21] and SCORPIO [22] spectral cameras mounted at the primary focus of the telescope. During operation with the ByuFOSC-2 the light detector was a CCD camera wi
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