Be star counterpart of X-ray pulsar MX0656-072
ATel #202; Manfred W. Pakull (Strasbourg), Christian Motch (Strasbourg) and Ignacio Negueruela (Alicante)
on 24 Oct 2003; 12:29 UT
Credential Certification: Manfred W. Pakull (pakull@astro.u-strasbg.fr)
Subjects: Optical, X-ray, Neutron Star, Star, Transient
Referred to by ATel #: 1293
The field of the pulsating transient X-ray source MX0656-072
(ATEL #197,#199)
has been observed with the ROSAT PSPC in 1993 September to
reveal only a close pair of sources just outside the 3' error region.
One, RX J065815.0-071237, coincides with the star
GSC2.2 S100221215. An optical spectrum reveals an early-K star with strong emission
reversals in the CaII H and K lines, i.e., an active chromosphere.
The position of the other ROSAT source, RX J065817.7-071228, is consistent
with the previously proposed counterpart, a variable reddened Be star
(V=12.05-12.38, B-V=1.02-0.86; Pakull 1978, The (ESO) Messenger 13,
17). The star is also H(alpha) emission line star No. 33 in the catalogue
of MacConnell (1981 A&AS 44, 387), it carries GSC2.2 designation S100221212 and is
located at (2000) 06:58:17.30, -07:12:35.3.
Repeated observations reveal a O9.7Ve spectral type displaying extremely narrow
(unresolved at a
resolution of 50 km/s) emission lines of HI, HeI and low-ionization metals.
Their strengths has strongly increased over the last few years.
These findings suggest a Be X-ray binary nature of MX0656-072.
