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Bright variable star discovered at VSA2005

 
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Reiner
Korisnik
Korisnik
Joined: 25 Aug 2005
Posts: 26
Location: Spain-Germany-Croatia triangle
PostPosted: Fri Aug 26, 2005 4:08    Post subject: Bright variable star discovered at VSA2005 Reply with quote

Hello,

the Photometry group of this year's VSA knows it already, so here it is for all others too Wink

Raoul Behrend from Geneva Observatory in Switzerland found an apparently new variable star on our photometry images of asteroid (381) Myrrha. Raoul helped us with the photometric reduction of the images and additionally checked all images for new variable stars. We imaged this asteroid on August 7.

The star is of visual magnitude 11 and thus pretty bright. The variability seems to be large too with an amplitude of about 1mag. Now it needs to be observed on a few nights and the period and amplitude and also the shape of the lightcurve must be determined to see what type of variable star it is. Because it is so bright, this could be done even visually with a 25-cm telescope or so. The telescope at OAM, Mallorca, which we used during the VSA, is pretty busy with photometry of asteroids that no time can be scheduled to get the lightcurve of this star, so it is your turn!

Re. (381) Myrrha, I observed it on two more nights from Mallorca, after the end of the VSA, and it seems as if the period known so far is wrong. The Harris-Catalogue ( http://cfa-www.harvard.edu/iau/lists/LightcurveDat.html ) gives 5.74h but with the one night from VSA2005 and the two I did later Raoul found a period of 6.57h, see: http://obswww.unige.ch/~behrend/page_cou.html

Search for (381) Myrrha there and click on the link.
BTW, Raoul's page gives the periods in days, so multiply with 24h/d to get hours!

Search for OAM2 on that page to find the provisional lightcurve for our VSA2005 variable star discovery and also the coordinates, to know where to look for it.

Ciao and good luck,
Reiner
OAM2s.jpg

Provisional lightcurve of OAM2, the variable star discovered at VSA2005

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Reiner
Korisnik
Korisnik
Joined: 25 Aug 2005
Posts: 26
Location: Spain-Germany-Croatia triangle
PostPosted: Sun Aug 28, 2005 18:28    Post subject: Finder chart for OAM2 Reply with quote

Hi,

I have made some finder charts for OAM2. It is pretty much south but can be observed well currently on the first half of the night from Visnjan, Zagreb, Belgrade etc.

The coordinates are: 19h52m35.72s -20°05'14.6"
North up, east left.

The closest star north of OAM2 on the wide-field chart is 9 Sge, mag 5.8 . It can also be seen on the detailed chart at the top. So you can find OAM2 even by starhopping.

For an introduction to visual observing of variable stars see e.g.: http://www.aavso.org/publications/manual/

Or this: http://www.rasc.ca/observing/variablestars/tutorial.html

Ciao,
Reiner
OAM2_finder_chart1.jpg

Wide-field finder chart for OAM2.

OAM2_finder_chart2.jpg

Detailed finder chart for OAM2. The box is the field of view of the 30-cm telescope at OAM, 28 arcmin x 28 arcmin.

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korado
Super Korisnik
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Joined: 20 Jan 2005
Posts: 498
Location: Visnjan
PostPosted: Mon Aug 29, 2005 23:33    Post subject: Reply with quote

Old Visnjan Observatory telescope refurbished, oiled, running....

Ana Bonaca and I managed to make some fifty images of the new variable star. As the star is a bright, exposition times 5 to 10 seconds.

Wide field at:
http://www.sci.hr/edu/2005/2005_VSA/OAM2_VO.jpg
OAM2_VOs.jpg

OAM2 - Visnjan Observatory photo insert 2005.08.29. 21:32 UT

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korado
Super Korisnik
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Joined: 20 Jan 2005
Posts: 498
Location: Visnjan
PostPosted: Thu Sep 08, 2005 22:38    Post subject: Reply with quote

As we have now more data for the light curve approximation and possible star classification, I made a web page in Croatian about the discovery:
/viewtopic.php?t=111
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Reiner
Korisnik
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Joined: 25 Aug 2005
Posts: 26
Location: Spain-Germany-Croatia triangle
PostPosted: Thu Sep 08, 2005 22:58    Post subject: OAM2 follow-up Reply with quote

korado wrote:
As we have now more data for the light curve approximation and possible star classification, I made a web page in Croatian about the discovery:
/viewtopic.php?t=111


As the star is on the evening sky already and moon is approaching too, follow-up must be done as soon as possible, to get a long run on each night, which is needed to exclude "aliases".

Reiner
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ljuban
Novi korisnik
Novi korisnik
Joined: 09 Sep 2005
Posts: 2
PostPosted: Fri Sep 09, 2005 11:43    Post subject: hey Reply with quote

Here I am back
Congratulations on successful images!
May computer came from service, now it works properly
I?m still in negotiations about the equipment but I hope it will be done in next week
Reiner, thanks for warnings:-)
Had anyone started writing something about Tergeste ect. Because I did some drafts and I?ll try to send it to all members of RtFM group as soon as possible (may be I want because it sound a bit strange) because I have now work to do with my Petnica project and the school just started but in a week I?ll be back on a track. So if there is anything I can do just name it:-)
Greetings

Ljuban
________
BUY EASY VAPE VAPORIZER


Last edited by ljuban on Sat Feb 12, 2011 9:11; edited 1 time in total
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Reiner
Korisnik
Korisnik
Joined: 25 Aug 2005
Posts: 26
Location: Spain-Germany-Croatia triangle
PostPosted: Wed Sep 21, 2005 15:27    Post subject: OAM2 observed last night at Mallorca Remo1 Reply with quote

Hi folks,

anyone observed OAM2 meanwhile? Petra, Ljuban, Maja, Alex?
I was not much observing recently, being too busy with other things,
but last night I used the bright full moon night, which is useless for
faint targets but good enough for something as bright as OAM2, and
I imaged it for about 3.5 hours.

Folks, within the next few weeks the lightcurve must be determined
otherwise we need to wait one more year.

*Maybe* I will be able to observe it the next nights too.
Anyone wants to volunteer as measurer? If so, please drop me
an email.

Ciao,
Reiner
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ljuban
Novi korisnik
Novi korisnik
Joined: 09 Sep 2005
Posts: 2
PostPosted: Sat Sep 24, 2005 11:46    Post subject: Yo Reply with quote

Here I am a volunteer:)
Send me those images on sleepwalker_bg@yahoo.com, I'll try to work on it as soon as possible.
As for observing on my one, there are still problems with getting to equipment, sorry:) hope you'll have nice weather!!!

Ciao
Ljuban
________
Hyundai Atos


Last edited by ljuban on Sat Feb 12, 2011 9:11; edited 1 time in total
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alexci
Novi korisnik
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Joined: 15 Jun 2005
Posts: 7
PostPosted: Sat Sep 24, 2005 19:43    Post subject: OAM2 Light curve Reply with quote

Hello,

Reiner imaged OAM2 last three nights. I downloaded the images and made photomerty of the star. I hope we will determine the light curve until December.
The period of the variable star is about 8.6 hours and the amplitude about 0.5mag.


Aleksandar Cikota
OAM2_abcdefghi.jpg

Light curve so far. Likely the type is WUma.

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alexci
Novi korisnik
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Joined: 15 Jun 2005
Posts: 7
PostPosted: Thu Oct 13, 2005 23:36    Post subject: Reply with quote

Hello!

Reiner imaged on 22nd September and 09th October OAM2 and we determinated the period. It is about 8.591h.
Some people know it and some not. I have got some time on the 0.5m f/8 IOWA Robotic teleskope in Arizona. Last two nights (11th and 12th October) I imaged OAM2 to fill the gap and determinate provsory the light curve form. The seeing wasn't god in the first night - on the LC you can see big errors. In the first night I imaged 2h 10m of period - every 10min one image and on the second night about 1h 40m. I will also try to image in the next nights to become a more precise LC.


Aleksandar
OAM2_resize.jpg

OAM2 light curve so far. The last two measurements were imaged from Arizona, USA.

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alexci
Novi korisnik
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Joined: 15 Jun 2005
Posts: 7
PostPosted: Thu Feb 23, 2006 22:34    Post subject: OAM2 --> X-ray source Reply with quote

Hello,


From the light curve, we can conclude that GSC 6321-798 (OAM2) is an eclipsing contact binary system of W Uma type.

An eclipsing binary star is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. In the case where the binary is also a spectroscopic binary and the parallax of the system is known, the binary is quite valuable for stellar analysis.
Eclipsing binaries are variable stars, not because the light of the individual components vary but because of the eclipses. The most notable eclipsing binary is the star Algol (β Persei), named the "demon star" by the Arabs in all probability because they noticed the variation in its light.
The light curve of an eclipsing binary is characterized by periods of practically constant light, with periodic drops in intensity. If one of the stars is larger than the other, one will be obscured by a total eclipse while the other will be obscured by an annular eclipse.

The period of the orbit of an eclipsing binary may be determined from a study of the light curve, and the relative sizes of the individual stars can be determined in terms of the radius of the orbit by observing how quickly the brightness changes as the disc of the near star slides over the disc of the distant star. If it is also a spectroscopic binary the orbital elements can also be determined, and the mass of the stars can be determined relatively easily, which means that the relative densities of the stars can be determined in this case.
In the study of stars, a contact binary is a type of binary star in which both components of the binary fill their Roche lobes. The uppermost part of the stellar atmospheres forms a 'common envelope' that surrounds both stars. As the friction of the envelope brakes the orbital motion, the stars eventually coalesce, unless something unusual happens.

Roche lobe
The Roche lobe is the region of space around a star in a binary system within which orbiting material is gravitationally bound to that star. If the star expands past its Roche lobe, then the material outside of the lobe will fall into the other star. It is an approximately tear-drop shaped region bounded by a critical gravitational equipotential, with the apex of the tear-drop pointing towards the other star (and the apex is at the Lagrange L1 point of the system). It is different from the Roche limit which is the distance at which an object held together only by gravity begins to break up due to tidal forces. Both the Roche lobe and the Roche limit are named after the French astronomer Édouard Roche.
Close to each star, surfaces of equal gravitational potential are approximately spherical and concentric with the nearer star. Far from the stellar system, the equipotentials are approximately ellipsoidal and elongated parallel to the axis joining the stellar centers. A critical equipotential intersects itself at the center of mass of the system, forming a two-lobed figure-of-eight with one of the two stars at the center of each lobe. This critical equipotential defines the Roche lobes. If you were to hypothetically fill these lobes completely with water, a ship could sail from one star to the other, passing through the point between the two stellar oceans where the tips of their sharp peaks touch (known as the Lagrange L1 point).
As such, the Roche lobe is one of two volumes of space in the system. These volumes are bounded by a particular surface of equal potential energy. The potential energy is calculated in a frame of reference that co-rotates with the binary system. Because this frame of reference is a non-inertial frame, the gravitational potentials due to the masses of each of the two stellar nuclei (which vary inversely with distance from the center of each star) must be supplemented by a pseudo-potential corresponding to centrifugal force. This pseudo-potential is proportional to the square of the perpendicular distance from the axis of rotation of the system.
Where matter moves relative to the co-rotating frame it will seem to be acted upon by a coriolis force. This is not derivable from the Roche lobe model as the coriolis force is a non-conservative force (i.e. not representable by a scalar potential).
When an object "exceeds its Roche lobe", its surface extends out beyond its Roche lobe and the material which lies outside the Roche lobe can "fall off" into the other object's Roche lobe. This can lead to the total disintegration of the object, since a reduction of the object's mass causes its Roche lobe to shrink. Overflow from the Roche lobe is responsible for a number of astronomical phenomena, including recurring novae (binary stars consisting of a red giant and a white dwarf that are sufficiently close enough together that material from the red giant dribbles down onto the white dwarf), X-ray binaries and millisecond pulsars.

W Ursae Majoris variable
A W Ursae Majoris variable is a type of variable star. These stars are close binary stars, whose surfaces are in contact with one another. They are termed common envelope binaries because they essentially share material in their outer layers.
The class is divided into two subclasses: A-type and W-type. A-type W UMa binaries are composed of two stars both hotter than the Sun, having spectral types A or F, and periods of 0.4 to 0.8 days. The W-types have cooler spectral types of G or K and shorter periods of 0.22 to 0.4 days.
Their light curves differ from those of classical eclipsing binaries, undergoing a constant ellipsoidal variation rather than discrete eclipses. This is because the stars are in physical contact and thus constantly eclipse one another, and also because the stars are gravitationally distorted by one another. The depths of the brightness minima are usually equal because both stars have nearly equal luminosities.
Contact binary systems are often an X-ray source.

I made a sectional view (with a ROSAT image over a EasySky screenshot) and we can see that OAM2 is an x-ray source also. Very Happy .

Regards,
Aleksandar
cobio_400.jpg

This is a model of a late-type contact binary, or W Ursae Majoris system. The color scale (from dark red to blue-white) maps increasing effective temperatures. The dark-red (= cooler) areas are dark spots, similar to, but much bigger than sunspots.

OAM2_curve_final_s.jpg

GSC 6321-798 (OAM2) light curve.
http://www.neznamadresu.com/IRO/oam2/OAM2.jpg

XRay_GSC_3s.jpg

http://www.neznamadresu.com/IRO/oam2/XRay_GSC_3.jpg

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alexci
Novi korisnik
Novi korisnik
Joined: 15 Jun 2005
Posts: 7
PostPosted: Sun May 07, 2006 20:10    Post subject: Reply with quote

Hi,

The lightcurve of GSC 6321-798 = OAM2 is finnished!

- period: 0.357973 ± 0.000002 day
- one principal minima: 2005-09-23.0954 ± 0.0008 UT at the barycenter of the solar
system
- peak to peak variability: 0.55mag
- type EW (=W UMa like)

Here is the final lightcurve:
http://www.neznamadresu.com/IRO/oam2/OAM2.jpg

and here is the lightcurve from Raoul Behrend (for comparison):
http://obswww.unige.ch/~behrend/rv00321a.png

Best regards,
Aleksandar
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