Central Bureau for Astronomical Telegrams
IAUC 3251: OPTICAL CANDIDATES FOR TWO X-RAY SOURCES; Aql X-1
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Read IAUC 3252
Circular No. 3251
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-864-5758
OPTICAL CANDIDATES FOR TWO X-RAY SOURCES
J. McClintock and C. Canizares, Massachusetts Institute of
Technology; W. A. Hiltner, University of Michigan; and L. Petro,
Hale Observatories, have found strong candidates for the x-ray
sources 4U 1755-33 and 4U 1543-62. Both candidates are within the
SAS-3 error circles and are labeled star No. 6 on the finding
charts published by Apparao et al. (1978, Nature 271, 225) and
Jernigan et al. (1978, Nature 272, 701). The stars show strong
ultraviolet excess on U and B plates obtained with the 400-cm
telescope at Cerro Tololo Interamerican Observatory in 1976 Mar. A
photoelectric measurement in 1978 June with the 150-cm telescope
gave B >~ 20 for the 4U 1543-62 candidate. A short-exposure spectrum
of the candidate for 4U 1755-33 was obtained in 1978 June with
the SIT vidicon on the 400-cm RC spectrograph and shows a flat
continuum with B ~ 19 to 19.5. A spectrum integrated for 2.5 hr with
the Shectman photon-counting spectrometer on the Dupont 250-cm
telescope at Las Campanas Observatory shows a featureless continuum
with no emission or absorption features from 3500 to 5200 A. A
preliminary inspection of the 3-A-resolution spectrum gives upper
limits of 1.5 A for the equivalent widths of any narrow emission
features at H-beta or He II 4686 A.
R. Griffiths, Center for Astrophysics, and the HEAO A3 group
report that the above candidate for 4U 1543-62 = 2S 1543-624 lies
near the center of their error box, which reduces the SAS-3 error
box by a factor of 3. Similarly, the above candidate for 4U
1755-33 = 2S 1755-338 is also confirmed by the HEAO A3 error box,
which eliminates the eastern half of the SAS-3 circle.
AQUILA X-1
D. Mook, M. Kurtz, J. Weed and M. Johns report that spectra of
the optical counterpart proposed for Aql X-1 have been obtained on
July 29 UT with the image-tube scanner on the 132-cm telescope at
the McGraw-Hill Observatory at about 6 A resolution. They confirm
the appearance of emission near 4640-4650 A and 4686 A as reported by
Puetter and Smith (IAUC 3243). Several spectra were obtained about
20 min apart. In some, these features were not obviously present,
which may explain why van Paradijs and Remillard did not detect
them with the same instrument (IAUC 3243). No H-alpha was seen on these
same spectra.
1978 August 8 (3251) Brian G. Marsden
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