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From: IAUC mailing list
Subject: IAUC 7022: 1998ec; XTE J1946+274

Circular No. 7022
Central Bureau for Astronomical Telegrams
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XTE J1946+274
P. Ghavamian, Rice University; and M. Garcia, Harvard-
Smithsonian Center for Astrophysics, write: "We report photometric
and spectrocopic measurements of the source suggested by Israel et
al. (IAUC 7021) to be the optical counterpart of the transient
x-ray pulsar XTE J1946+274. Spectroscopy (integration time 50 min;
spectral resolution 0.6 nm; range 350--750 nm) was performed on
Sept. 27.1 UT with the 1.5-m telescope (+ FAST spectrograph) of the
F. L. Whipple Observatory at Mt. Hopkins, using the position
reported by Israel et al.. Two point sources appear near that
position on the Digital Sky Survey, both of which were covered by
the slit (p.a. 90 deg). The ratio of the H-beta/He I 447.1-nm/H-
gamma lines indicates a spectral type of B2 (+/- 2 subclasses) for
the brighter of the pair, which is located at R.A. = 19h45m39s.26,
Decl. = +27o22'45".3 (equinox 2000.0; +/- 0".3). Interstellar
absorption lines at 577.8, 589.0 (Na D), and 628.4 nm are very
prominent, with EW = 0.09, 0.2, and 0.18 nm, respectively. The
fainter star lies approximately 7" to the west of the brighter one.
The ratio of the Balmer series and Mg b absorption lines in the
fainter star suggests a spectral type of F9 +/- 1. The FAST
spectra of the B star fail to show the weak H-alpha emission
reported by Israel et al.; instead, H-alpha absorption is seen with
EW = 0.68 nm. Photometry was performed on the B star using the CCD
imager on the 1.2-m telescope at Mt. Hopkins on Sept. 28.1. Using
Guide Star Catalog magnitudes for flux calibration, we find V =
14.4 +/- 0.3. The lack of emission lines and variability does not
necessarily discount this star as the optical counterpart of XTE
J1946+274. The strength of the Na D line indicates that the
brighter star is approximately 4000 pc distant, and implies A(V)
about 8. If this star is the optical counterpart of the x-ray
pulsar, the x-ray spectrum should show substantial low-energy
absorption (N_H about 1.5 x 10E22 cmE-2)."

(C) Copyright 1998 CBAT
1998 September 28 (7022) Daniel W. E. Green