[vsnet-chat 4579] EW Lac: a bright northern "radio variable" Be star of large visual amplitude

[Thom Gandet <tgandet@mindspring.com>]

    EW Lac (=HR 8731) is a very interesting and bright (V=5.33) with a
photometric range of V=5.22 to 5.48 (p=5.00-5.300).  This should be
detectable using the kind of precision visual photometry practiced by
Sebastián Otero and others.  Short periods observed in the photometry
are 8.7 hrs, 15 hrs, and 19.2 hrs.

    The spectrum shows the non-radial pulsation line profile changes
typical of some Be stars, notably Delta Sco.  The spectral type is
B3III-IVpeV, although it appears to vary with time.

    EW Lac is only one of two Be stars which may be variable at the
2 cm radio wavelength.  It also has a very high radio spectral index,
indicating that the radio emission does not arise in thermal radiation
from ionized gas, which is the mechanism giving rise to the far-IR,
millimeter and radio emission from "normal" Be stars.

    The coordinates of EW Lac are:
       RA: 22h 57m 5s   Dec: +48° 41' 3" (Epoch 2000)

    Suggested comparison stars for visual observation are 5 And
(V=5.70, B-V=+0.44) and 7 And (V=4.54, B-V=+0.28).  There are no
close stars similar in color to EW Lac that could be used for
visual estimates.

    Good observing!

Cordially,
Thom Gandet


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                      Thomas L. Gandet, Director
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