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Date and Time of the Query: 2022-01-25 T07:20:14 PST
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Notes for object MESSIER 092

2 note(s) found in NED.


1. 2001A&A...368..137V
Re:NGC 6341
3.28 NGC 6341/M 92
A short PSPC observation of this cluster has been published by
Johnston et al. (1994), and longer HRI and PSPC observations by
Fox et al. (1996). I analyze the two HRI observations separately, determine
the offset between them, and then analyze the co-added image, to find
positions which differ markedly from those listed in the earlier papers.
In agreement with Geffert (1998) I identify two X-ray sources in the HRI
field of view with optical objects, viz. XE with the W UMa variable
V798 Her (V14 of Hachenberg 1939), whose accurate position is given by
Tucholke et al. (1996), and X10 with TYC 30815101 from the Tycho Catalogue
which also has an accurate position. The binary period of V798 Her is
0.346 d, and from this I estimate M_V_ ~ 4.5; with the observed magnitude
V = 14.5 a distance of order 1 kpc follows, and the observed countrate then
corresponds to a luminosity between 0.1-2.4 keV L_x_ ~ 10^30^ erg s^-1^,
quite reasonable for a contact binary (see, e.g. McGale et al. 1996). XE is
detected only in the longest PSPC and in the longest HRI observation;
compatible with a constant flux. Geffert (1998) suggests on the basis of
its colour that TYC 30815101 is a G star; it would then have an X-ray
luminosity high but not unreasonable for a G main sequence star (see Table
A.1). Its X-ray flux increases by about 40% between April 1994 (HRI
countrate 25.6 +/- 1.3 cts ksec^-1^) and April 1995 (HRI countrate
43.2 +/- 4.1 cts ksec^-1^); its countrates in the long PSPC observation of
1992 are 54.8 +/- 1.1 and 106.7 +/- 1.6 cts ksec^-1^ in channels 50-240 and
11-240, respectively; the large countrate in the lower channels indicates
that interstellar absorption is low, as expected for a stellar X-ray
spectrum at the small distance of the optical counterpart. Thus, the X-ray
countrates are compatible with the suggested identifications for XE and
for X10.
From these two objects I determine the offset - given in Table 1 -
between the X-ray coordinates and the optical coordinates, and apply this
to the X-ray coordinates to obtain the positions given in Table 2. The
source numbering in the table is after Johnston et al. (1994) and Fox
et al. (1996). The offset determination is dominated by X10, because of its
accurate position on the X-ray detector (error {DELTA} in Table 2). The
estimated errors in the offset are 0.6" in right ascension and in
declination; combining these with the error in the position on the detector
of source X8, I estimate that the position of X8 is accurate to 1.5",
comparable to the accuracy obtained by Geffert (1998). Note, however, that
for non-identified sources the HRI positions given in Table 2 are more
accurate than those given by Geffert (1998), which were based on PSPC
positions.
The PSPC countrate of X8 is 3.0 +/- 0.7 cts ksec^-1^ (channels 50-240)
in the short PSPC observation, compatible with expectation on the basis of
its HRI countrate; during the long PSPC observation it is substantially
higher, at 6.5 +/- 0.4. The source also has an appreciable countrate in the
softer channels, and a bremsstrahlung fit is shown in Fig. 3. If we set
N_H_ = 10^20^ cm^-2^, as estimated from the visual absorption of the
cluster, we cannot obtain a good fit; the absorption to X8 requires
N_H_ ~ 2.5 x 10^20^ cm^-2^. The spectrum is soft, with a bremsstrahlung
temperature kT = 1.1 +/- 0.2 keV.
It should be noted that the identification of X8 (called source C in
Fox et al. 1996) with an ultraviolet object UV 8203 by
Ferraro et al. (2000) is based on the old, inaccurate positions of
Fox et al. (1996), which are incompatible both with the improved positions
of the PSPC sources by Geffert (1998) and of the HRI sources in this paper.
These positions indicate that the proposed identification is not acceptable.

2. 1918PLicO..13....9C
Re:NGC 6341
Bright, unusually condensed globular cluster; cluster about 10' in diameter; the
bright central portion 2'. M. 92. 24 s.n.


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