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Special Notice #280: HST UV spectroscopy observations of S Dor scheduled

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May 9, 2012: We have been informed by Dr. Noel Richardson, Georgia State University, that the UV spectroscopy observations of S Dor to be made with the Hubble Space Telescope have been scheduled for

2012 MAY 11 from 21:21:55 UT to 23:55:04 UT.

During the 24 hours prior to and following the HST observations, as well as during them, please increase your visual/BVRI (or as many of these filters as you can) coverage from once per night to twice per night. Afterwards, please return to nightly observations until further notice.

The HST observations of the luminous blue variable prototype S Dor are part of the multiwavelength, multisite campaign described in AAVSO Alert Notice 453 ( As mentioned there, the campaign is to study the photosphere of this star. Optical spectroscopy from CTIO and an amateur in Australia have already been obtained successfully. Approval is still pending for near-IR spectroscopy from SOAR and mid-IR photometry from Gemini.

It is important to continue the excellent monitoring you have been carrying out. Your observations are not only very interesting but also necessary to correlate all of the observations and interpret the variability taking place in S Dor. S Dor is particularly interesting at present because its current state allows the deepest look into its photosphere since the 1960s, leading to a better understanding of its stellar and wind properties. To quote Dr. Richardson, "...the types of variability we are really wanting to probe are the long term trends and the decline to optical minimum it is going through."

Visual and photometric observations are requested on a nightly or twice-nightly basis as described above. BVRI photometry would be ideal, but any filter(s) would be very helpful. According to observations in the AAVSO International Database, S Dor has brightened from visual magnitude ~10.4 in February 2012 to its current value of 10.0. Its decline from visual magnitude 9.2 began in 2006, with a more rapid decline starting in early 2010.

Coordinates: RA = 05 18 14.35  Dec = -69 15 01.1 (2000.0)

Charts may be created using VSP (

Please submit observations to the AAVSO International Database using the name S DOR.

This campaign is also described on the AAVSO Observing Campaigns page (

Your observations are key to the success of this campaign. If you have been observing S Dor, please continue. If you have not, and if you can observe this far south, please add S Dor to your nightly list. Many thanks!

This AAVSO Special Notice was prepared by Elizabeth O. Waagen.

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