The Variable Star Observers Switzerland (VSOS) is a working group of the Swiss Astronomical Society. The members are engaged in the observation and the recording of the changing brightness of variable stars.

Latest activities

Class Type Star Datasheet Observation
RS Recurrent Nova RS Oph   HIM (J. Schenker):      


October 10, 2021:   Robert Glaisen (Observatory Simplon Adler SIM) recorded the star V409 And of ZZO Ceti type. These types of stars have a low variabilty in brightness and short periods up to 40 minutes. Their spectra include HeII and CIV absorption lines. See Report.
June 13 - 15, 2021:   Robert Glaisen (Observatory Simplon Adler SIM) recorded the brightness of AU Coronae Borealis, a rare type of a pulsating variable star: An accreting subdwarf in a binary star system (SXPHE). The analysis of the 435 pictures (exposure time 40 sec. each) shows, that its variation in brightness varies between 0.13 and 0.22 mag (acc. literature: 0.2 mag). Also the period of the variation remains not constant, but varies between 68.8 - 77.5 min. (acc. literature: 74.5 min.). Probably, a second period is overlayed? See Report.
December 18, 2020:   Robert Glaisen (observing station BRI) recorded the brightness of DY Pegasi, a rare type of a pulsating variable star: An accreting subdwarf in a binary star system (SXPHE). During a period of 105 minutes, the star varies its apparent brightness by 0.55 mag. See Report.
Begin Nov. 2020:   Call for observation: Exoplanet K2-34b
For more information please see Project Phoenix
May 30, 2020:   During winter 2019 / spring 2020, the semi-regular pulsating supergiant Beteigeuze showed an extraordinary drop of its brightness. Hendrik Pruijs (observing station VIL), recorded the brightness of alpha-Orionis during numerous nights. Please follow the preliminary results. Coming winter, the recordings will be continued...
Jan. 29, 2019:   Announcement: 2. Workshop about the observation of Exoplanets: The observation of variable stars goes into a new round: In addition to the classical variable stars, the observation of exoplanets also falls under the category of variables. After the first transits of exoplanets have been successfully analyzed and the results have been transmitted to an international database, we want to incorporate the gained experience and insights into the following observing campaigns and to optimize the workflow.
For more information please consult the detailed invitation.
Dec. 31, 2018:   Great success: Franziska Friedli submitted her graduation diploma work with the title "Reise zur Andromeda-Galaxie - Photometrische Entfernungsbestimmung zum Cepheiden M31-V1". The excellent work was top graded. Congratulations!
April 30, 2018:   New observation of a Close Binary Eclipsing System: Hendrik Pruijs recorded RW Tau during 3 months. Thanks to his numerous measurements, it was possible to define the Time of Minimum and the Period of RW Tau with an uncertainty of only +/- 0.00003 days. See report and measurements.
April 10, 2018:   New observation of a Close Binary Eclipsing System: Dieter Hofer recorded AM Leo and created a lightcurve.
March 3, 2018:   Meeting with Exoplanet Workshop at the Observatory Zimmerwald, considering the data reduction using the software AstroImageJ.
Invitation,  Protocol,  Script part A,  B,  C,  D
Jan. 21, 2018:   Practical for planning: A new "Time of Minimum" calculator is available. Knowing the epoch and the period of a variable star, the excel sheet calculates the times of the 30 coming minmium phases, starting from any date.
Jan. 15, 2018:   Announcement: Workshop for Observation of Exoplanets. As announced recently, the team around the Sonnenturm in Uecht has already achieved some great success and made the results available to an international headquarter. The point now is to intensify and consolidate our previous observations. That's why we meet us to the Exoplanet Workshop at Zimmerwald Observatory. For more information, please consult the Invitation.
Dec. 21, 2017:   Great success: Anna Friedli, already known for her observations of exoplanets, submitted her graduation diploma work with the title "Ferne Welten - Transitbeobachtungen von Exoplaneten". The excellent work was graded with an award and laudation. Congratulations!
Dec. 17, 2017:   New observation of a Close Binary Eclipsing System: Hendrik Pruijs recorded X Tri and created a lightcurve. Ulrich Grebien wrote the corresponding datasheet.
Oct. 17, 2017:   A new issue of the BAV-Journal was published. Editor: Lienhard Pagel.
Oct. 16, 2017:   Again: The station SON (Sonnenturm: Thomas Friedli, Anna Friedli and Patrick Enderli) confirmed an exoplanet! During a 127-minute observation campaign, a planet passed the star HAT-P-23. The planet, called HAT-P-23b, caused a decrease of the brightness of the star of just 0.0169 mag, but this could certainly be proved. Congratulations!
Further observation details can be found here.
Aug. 5, 2017:   Thomas and Anna Friedli observed the exoplanets "Qatar-1 b" and "HAT-P-36 b" with the Robotic Solar Observation Telescope (roboSOT), which is installed on top of the Sonnenturm at Uecht near Niedermuhlern. For the successful recording, the transit method was applied. Congratulations!
July 24, 2017:   Ulrich Grebien developped a practical data sheet, making the planning, observation and recording of Variables more easier. Each of the sheets is made for a certain variable Star and contents general information, reference stars, finder charts, time of minimum and period calculator.
June 20, 2017:   The VSOS goes online.
May 23, 2017:   Workshop with Hendrik Pruijs about the determination of the brightness of a star, using the software AstroImageJ.
Feb. 13, 2017:   Lecture with Ulrich Grebien about Variable Stars.