Sat, 07/07/2018 - 15:24
Hi
last night i captured a pic from altair and its vicinity in AQUILA.
cam:ZWO 1600 PRO tel:120 mm apo sky watcher
i noticed a star in pos: 19 51 57.5 +08 42 54.8(Mean J2000)
its mag was 12(almost).
I refered to catalogus in CARTES DU CEIL Program.it was no star brighter than 17 in that position.
in simbad catalog it name is RAFGL 5000.
MY question: is it a new variable?
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altair6.jpg1.9 MB
Hi Abdolreza,
AS expected from its presence in the RAFGL catalogue, this is a red giant. It is an OH star and maser source, an evolved object. These are usually embedded in a coccoon and are very red (J-K in 2MASS is 2.78) and only visible in the infrared. It is always important that you mention the passbnd used in your observations.
I assume you use an unfiltered CCD and since they have a peak response at red wavelengths, it is usual that they detect these red objects that are not bright in the visible.
The star is also IRAS 19495+0835, EIC 1301, 2MASS J19515771+0842545 (an infrared source) and USNO-B1.0 0987-0515747.
The best position comes from Gaia DR2: 19 51 57.71 +08 42 54.7 (J2000.0).
(Always use VizieR to get data from all available catalogues, do not trust planetarium software without mentioning actual data sources).
The brightest catalogue magnitude is r= 15.7 in Pan-STARRS1, this translates to approximately 17 in V. Most of the time the object will be fainter.
Finally, and most important, we still have some red and miscelllaneous ASAS-SN variables to add from the ASAS-SN catalogue published by the end of last year and this star is one of them:
https://asas-sn.osu.edu/database/light_curves/64182
It is a long period mira as most OH stars are (classified as L by the ASAS-SN software).
The points around V= 17.4 are contamination form nearby stars. The true range is 15.7 - <17.5 V. I will add it to VSX since it requires a resvision.
Cheers,
Sebastian
Thanks