Affiliation
Royal Astronomical Society of New Zealand, Variable Star Section (RASNZ-VSS)
Fri, 08/19/2016 - 10:06
This star is type LB Range 10.7-12.3B. It has 71 observations listed by 2 observers but all of them are 0.0. Can anyone explain why?
Thanks
Stephen [HSP]
Hi Stephen,
Thanks for asking about the RS Lup data. The magnitudes for RS Lup are 0.0 because when the observations were made, only a letter sequence was available for the star. Measured magnitudes were not available for the comparison stars chosen, so each was assigned a letter. When an observer made an estimate, s/he used these lettered comps and recorded the magnitude as, e.g., <C or 7DV3E. Numerous stars in the RASNZ observing program had only letter sequences because of the relative lack of published photometry for Southern stars in those days. Both of the observers (Danie Overbeek and Tom Cragg) were using the RASNZ sequence for RS Lup.
When we digitized the observations, we could not put these letter magnitudes (what we also called step magnitudes) into the magnitude field. We put a 0.0 to indicate there was no numerical magnitude, and included the letter step sequence in the Commentcode or Comment field.
To convert these letter step magnitudes to a number, we need to find suitable measured values for the lettered comparison stars. Nowadays, that is not as difficult as it was even 10-15 years ago (let alone 20-30 years ago or more!). Over the years, the RASNZ has published numerical sequences for many of their letter sequences, and we have converted many magnitudes.
There are still several stars with letter step magnitude data in the AID; converting as many of these magnitudes as possible to numerical values is one of our projects. We will check to see what additional RASNZ sequences are available for these stars - we haven't done this for a while, so your question is a good reminder. Thanks!
Good observing,
Elizabeth Waagen
Thanks, Elizabeth. I remember those days in the RASNZ. A lot of my observations made nearly 50 years ago used only letters.
Kind regards
Stephen [HSP]
Thanks, Elizabeth. I remember those days in the RASNZ. A lot of my observations made nearly 50 years ago used only letters.
Kind regards
Stephen [HSP]
Hi Stephen,
Somehow I got disconnected from the various fora and was resetting my link after an email from Elizabeth. Saw the Pukemaru label. But this star looks a difficult object visually from the ASAS3 measures - amplitude of 0.5 and little regularity, although the maxima are well defined. I see it's a carbon star although the GCVS B maximum of 10.7 and the ASAS of ~9.0 don't really support that, giving a B-V of ~1.7. It would be worth a look in UBV to see what the colours really are - maybe there's a companion there somewhere.
Regards, Stan