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IAUC 4051: EXO 1846-031; 4U 1624-49; mu Cen

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                                                  Circular No. 4051
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM    Telephone 617-495-7244/7440/7444

EXO 1846-031
     A. N. Parmar and N. E. White, EXOSAT Observatory, European
Space Agency, communicate: "During a slew maneuver on Apr. 3 EXOSAT
detected a new bright x-ray transient.  A pointed observation
the next day gave a position for this source of R.A. = 18h46m39s, Decl. =
-3deg07'34" (equinox 1950.0), with an error radius of 15"; the
source was not variable during the 2-hr observation and had a flux
of 0.2 Crab.  The spectrum below 10 keV was extremely soft (kT ~ 1
keV) but has a high-energy power-law (~ 1.0) tail that extends out
to at least 25 keV.  The low-energy absorption is 3.5 +/- 0.5 x 10**26
H atoms/m**2.  A further EXOSAT observation will be made during Apr.
21.12-21.38 UT.  An optical search of the error circle is urged."

4U 1624-49
     M. G. Watson, R. Willingale, and A. R. King, University of
Leicester; J. E. Grindlay, Center for Astrophysics; and J. Halpern,
Columbia Astrophysics Laboratory, report: "Observation of this
object with the EXOSAT Observatory during Mar. 25-27 has shown the
presence of intensity dips in its 2-10-keV x-ray light curve that
recur with a period of 21 +/- 2 hr, presumably the binary period of
this system.  The dip pattern in each cycle lasts from 6 to 8 hr
and has a complex and variable structure, making a more accurate
period determination difficult.  4U 1624-49 is the seventh x-ray
source to have shown such periodic intensity dips (IAUC 4039,
4044); the periods of the other six objects are all below 8 hr."

     G. J. Peters, Department of Astronomy, University of Southern
California, writes: "CCD spectroscopic observations with the coude-
feed telescope at Kitt Peak National Observatory have revealed
that the recurrent, transient, Be-type star mu Cen abruptly developed
HS emission between Mar. 25 (H-alpha pure absorption) and Mar. 27
[centrally reversed H-alpha, V < R, R < I(cont)].  The onset of this
new emission episode was accompanied by rapid variability (10-20
min) in the profile of He I 667.8 nm.  By Mar. 30 the H-alpha emission
had definitely increased in strength [V = R >= I(cont)].
Additional observations of all types are urged during the initial
stages of this star's latest emission-line phase."

1985 April 15                  (4051)              Brian G. Marsden

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