Teams / Southern Gems / A first chart, actually a multi-star chart
*Sky & Telescope Illustration by Casey Reed
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International Year of Astronomy | American Association of Variable Star Observers (AAVSO)
Hi Sebastian, I really like the idea of putting as many on one sheet as possible and using less paper. I have a question. How do people know which of the comp stars to use for each star. Should they use only the ones that are close to the variable star or can they use any on that page? I think putting all the star information on one chart is also a good idea. I think that is the page that I was supposed to be doing. Is all the necessary information I will need already in previous posts? I thought I would make the chart and then let the group check what I have and see if we need to change or add anything. I will get busy on trying to do this today. What program can I use that is simple for making the chart? All Southern Gem members, please give input about whether you like having as many stars as possible on one sheet...any pros or cons that you might think of. We want to make this the best we can. We need your advice and thoughts. Cheers, Joan
Hi, Joan,
>>> Should they use only the ones that are close to the variable star or can they use any on that page?
The sequence for each variable is made up of the stars close to it.
The actual distance in the sky between some of the sequences is too large for a reliable estimate. E.g. We can't estimate VPuppis using the 48 comp star of the RCarinae sequence.
Or it would be extremely difficult to use the 35 comp star of the l Car sequence in Vela to estimate beta Doradus. It wouldn't make sense either, since each star has suitable comp stars nearby. So the answer is yes, use only the ones close to the variable because that makes the task much easier. Having to change between the variable field and the comp star field (using memory) is not recommendable. Sometimes I use the 36 inVolans to estimate lCar but that is the only star that may work for both the lCar and beta Dor sequences. I recommend using only nearby stars.
>>> I think putting all the star information on one chart is also a good idea
When you say "chart" do you mean "table"?
Just use the word chart to refer to our sky maps or it will be confusing.
I think we have given all the info already while discussing the list of stars. Magnitude range, type, period. I don't think more data are needed. The data: alpha Ori Semirregular 0.2 - 1.1 420: l Car Classical cepheid 3.32 - 4.12 35.562 beta Dor Classical cepheid 3.41 - 4.08 9.8426 eta Aql Classical cepheid 3.49 - 4.30 7.1769 R Car Mira 3.9 - 10.5 309 kappa Pav Pop. II cepheid 3.91 - 4.78 9.082 zeta Phe Eclipsing binary 3.94 - 4.42 1.6698 X Sgr Classical cepheid 4.22 - 4.86 7.0129 W Sgr Classical cepheid 4.28 - 5.07 7.5950 V Pup Eclipsing binary 4.35 - 4.92 1.4545 R Dor Semirregular 4.8 - 6.6 338 Maybe we can add some general info on each star. Alpha Orionis is named alpha but only a couple of times in history has actually been brighter than beta (Rigel) Orionis. l Carinae is one of the more luminuous cepheids known and it is the brightest one (after Polaris) in the sky if we take apparent magnitude. Beta Doradus is only 0.1 mag. fainter and follows l Car in the ranking. Classical cepheids are massive Population I (young) stars. Eta Aquilae was the first cepheid discovered. Pigott found it in 1784 (before delta Cephei discovery by Goodricke). R Carinae has to be observed with three different instruments if you want to cover its entire cycle: naked eye, binoculars and telescope! Kappa Pavonis is by far the brightest example of a Population II (old) cepheid. Low mass stars less luminous than classical cepheids. Kappa Pavonis display abrupt period changes. Continuous monitoring helps tracking them. Zeta Phoenicis is an Algol-type eclipsing binary. You will find the star at maximum brightness most of the time, so catching an eclipse will require patience but will be rewarding. When you are observing X Sagittarii you are observing the Milky Way center. Actually it is 1 degree South of X Sgr. W Sagittarii is a triple system mde up of the cepheid, a close F5 dwarf and a more distant A0 star. V Puppis is an eclipsing binary of the Beta Lyrae type. Brightness changes are continuous due to the ellipsoidal shape of the components. R Doradus is a semirregular star showing two maxima and strong amplitude changes from cycle to cycle. One of the largest stars with a diameter measured interferometrically from Earth (along with Betelgeuse, the other semirregular on our list) Cheers, Sebastian.
Sebastian, Thanks for the explanation about use of comp stars. I thought that was the case, but I wanted to clarify this. I will call the document with all the star information the table from now on. Thank you for putting all the information on there. The numbers for the periods...are all of those days or are any of those for hours or years? I agree that is everything we need, except that I will also add the observing months to this table as well. I am going to use that horrible program that I hate, Microsoft Excel. Haha. I should have this ready to send to the group by tomorrow for everyone to check. Cheers, Joan
Hi Joan, Sebastian I think the I Car chart Sebastian attached is fine. If you want a closer look at one of the variables and its comparison stars you can zoom in a little anyway. I must say that I do favour the simplicity of the 10-star charts. For example, I've found the Eta Aql chart to be nice to use and the brief description at the end (page 14 of the 10-star tutorial) to be sufficient. Regards, David
.. which brings the question of the charts for eta Aquilae and alpha Orionis, stars common to both the Northern and the Southern lists.
Do we want our own charts or just copy the ones from the Northern tutorial?
Cheers,
Sebastian.
Hi Sebastian, I think it's fine to use the ones from the Northern tutorial. It will save you a bit of time. Cheers, Joan
i think it is okay to have a couple of mutual stars.