[vsnet-alert 8626] Probable optical counterpart of XTE J1818-245

[Daisaku NOGAMI]

Dear colleagues,

D. Steeghs reported a probable candidate of the optical counterpart
of currently active X-ray transient XTE J1818-245, which is at
18h18m24s, -24o32'18" (J2000.0).  The R magnitude was ~17.5 at about
2005 Aug 18.00 (UT).  A finding chart is available at

http://hea-www.cfa.harvard.edu/~dsteeghs/Images/XTEJ1818-245.jpg .

Spectroscopic confirmation of this candidate and follow-up
observations in all the wavelengths and in all the methods are
strongly encouraged!

Best regards,
Daisaku Nogami
VSNET Collaboration Team

Begin forwarded message:

Date: 18 Aug 2005 03:25:51 -0000
From: atel at astronomerstelegram.org
To: nogami at kwasan.kyoto-u.ac.jp
Subject: ATel  585. ***Instant Email Notice***: Request for Observations 


***Instant Email Notice***: Request for Observations

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The Astronomer's Telegram                   http://www.astronomerstelegram.org 
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ATEL #585							     ATEL #585

Title:		Optical counterpart candidate to XTE J1818-245
Author:		D.Steeghs, M.A.P.Torres (CfA), W.Pych (CAMK,Warsaw), I.Thompson
		(Carnegie)
Queries:	dsteeghs at cfa.harvard.edu
Posted:		18 Aug 2005;  3:25  UT
Subjects:	Optical, X-ray, Binaries, Black Holes, Transients

We report on the likely optical counterpart to the X-ray transient XTE
J1818-245   (ATEL #578,#579).

Photometry was acquired with the Swope 1.0m telescope (Las Campanas
Observatory,   Chile) during August 17 2005 23:19 UT - August 18 2005 00:18
UT. Our observations   consist of several 60/180s exposures in the R and
V bands acquired with an image   quality of 1.3 arcsec.

Comparison of our images with the Digitized Sky Survey and 2MASS
reveals the   presence of a single new point-like object within the error
circle for the RXTE PCA   X-ray position reported in ATEL #579. The coordinates
for this optical source are   R.A(J2000): 18:18:24.4, Dec(J2000): -24:32:18.0
based on astrometry relative to the   2MASS frame (estimated uncertainty
0.3 arcsec). A comparison with nearby USNO stars   suggests a magnitude
near R=17.5.

We tentatively identify this object as the optical counterpart to
XTE J1818-245.   Follow-up photometric observations and the acquisition
of a spectrum to confirm the   optical counterpart are encouraged.

A finding chart for the candidate may be found at:      http:/hea-www.cfa.harvard.edu/~dsteeghs/Images/XTEJ1818-245.jpg

R-band finding chart for XTE J1818-245: http://hea-www.cfa.harvard.edu/~dsteeghs/Images/XTEJ1818-245.jpg
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