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(fwd) Re: RASNZ RS Oph sequence etc From: "Stan Walker" <astroman@xtra.co.nz> Date: Wed, 14 May 2003 08:28:45 +1200 Subject: [vsnet-chat 6329] Re: RASNZ RS Oph sequence etc Hi Brian and Sebastian, Comments about the RS Ophiuchi sequence on the RASNZ VSS chart are a little disconcerting especially as some of the comparison stars were measured at Auckland Observatory by Brian Marino and I. However, these values were not used by the VSS. The same applies for HL Canis Majoris where a very poor alternative sequence was used. During the 1970s and 1980s many sequences were measured photoelectrically at Auckland Observatory by Barry Menzies, Peter Gordon and others. Whilst the values were rounded to a tenth of a magnitude the accuracy is much better. >From 1972 all measures were transformed to the standard system using values determined from early measures of E Regions. The 'standard' stars were less accurate, but from Royal Observatry Bulletin #64, which contained many measures made by Cousins, Stoy and others at Cape. The ROB 64 measures were used widely in the Yale Bright Star Catalogue and are quite good for the era, ~1-2%. The AO values probably represent 2-3% photometry down to V = 10, with a gradually increasing error to about 10% at V = 14. Sequences from some other observers used by the VSS are variable in quality. Those from Mt John and Vogt are good, with the occasional misidentifications which have, presumably, been corrected. Others are not so good. From what we can see the HL CMa sequence was made with untransformed V filters only and did not allow for the dramatic sky variations as a function of distance from Sirius. I am surprised at the problems with the Webbink values - I hope this is not too widespread. The AO abandoned the sequence programme some time in the 1980s due to a variety of arguments over whose sequences were more reliable and turned to other regions where the work was appreciated more. One of the problems which obviously still troubles astronomy to the present day is that many people think that given a detector and a 'V' filter you can produce accurate photometry without much effort. As well, there is reliance upon two colour surveys which have their shortcomings. It would be great if anyone making charts for visual observers took a reasonably comprehensive course in practical photometry. Or, as Mike Simonsen is showing the value of, used measures only from people who know what they are doing. With people such as Sebastian who are striving for higher visual accuracy it would be nice to have the original two decimal place values for the AO sequences. But I think that this is just a dream. Regards, Stan PS. The photoelectric equipment at AO up until Mt John really got going in the 1980s was the best in NZ. We used a 50cm Zeiss reflector, with EMI 9502 pm tubes and a photon-counting system designed and built by Bruce Griffiths and Rodger Freeth at the University of Auckland. In spite of being in a city the photometry was good - we once used offset photometry to reach V = 16.24 with quite creditable accuracy and routinely worked on CVs at around 13-14. Unfortunately serious research there ceased in 1990 and little has been done in Auckland since, except for a very active group of people who work from their own observatories around the city.
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