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SW Lacertae

SET's picture
Joined: 2010-07-23

I wanted to share with you all one of my favorite late summer and autumn visual eclipsing binary stars. SW Lac is a great star for smaller telescopes. I don't quite agree with the range on the chart. I have been observing this star for years and I get a range of about 8.8 to 9.4. The star is very easy to locate by star hoping.It is directly south of Omi And, just over the border with Andromeda. The star pattern is so easy to recognize because it looks like a "hockey stick".


I have attached a "b" chart for SW. If you use a refracting telescope with diagonal, or a schmidt/cas scope, print of a reversed "b", "bR" from the VSP chart plotter. Have fun with this one. All the action takes place in about 3 hours. Times of minima to about 20 minute accuracy can be found on the 2012 AAVSO Eclipsing Binary Ephemeris on  the AAVSO web site.


Chris Stephan   SET

Robert Clyde Observatory

Sebring, Florida  USA

SW Lac b chart.png61.26 KB
SW Lac spot variability
Sebastian Otero
Sebastian Otero's picture
Joined: 2010-09-19

Hi, Chris,
I hope you are active again after your health problems!

The discrepance with the chart magnitudes (taken from VSX) and what you observe is probably due -in part- to the intrinsic variability of the star caused by spots.

The catalogued range was actually brighter than what was seen over the last decades. More spots, fainter magnitudes. During the Hipparcos mission, the brighter magnitude was V= 8.66 with V= 9.45 at minimum. In a 2004 paper (Albayrak et al, 2004A&A...420.1039A) focused on the star, the maximum magnitude faded from 8.54 to 8.61 between 2001 and 2003 and the minimum magnitude was as faint as V= 9.49.


SW Lac
kevinbalton's picture
Joined: 2011-09-26


Agreed, SW Lac is a great starting point for visual as well as photometric observers.  The last time (01Oct2005 - 18Nov2005) I targeted this W UMa binary the lightcurve varied (Vmag) from 8.55 to 9.45 which are similar to the values published earier in the decade.  W-D modeling (Alton & Terrell 2006) of V- and R-passband lightcurves from this epoch suggested the appearance of a cool spot which produced asymmetry (Max I < Max II) at maximum light.  Hot or cool spots on W UMa variables often make it difficult to nail down an absolute value for maxima or minima.




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