urgent observation request for TYC1799 1159 1

urgent observation request for TYC1799 1159 1

Postby Ulrich Bastian » Tue Mar 09, 2021 3:14 pm

Dear forum members,

back in January, the bright star TYC 1799 1159 1 (9th-magnitude in the red wavelength range; in the visual range it is about 10th magnitude) was serendipitously discovered by a German amateur to be an eclipsing binary. In the night to March 7, a second minimum was observed, so the fact is confirmed. However, the character of the light curve (period, depth of the eclipse, shape and width of the minima), together with the parallax and HRD location from Gaia eDR3, makes it an astrophysical impossibility. No conceivable combination of two stars could produce this whole set of characteristics. This conundrum could possibly be solved by assuming that the system contains a component radiating predominantly in H-alpha - e.g. an accretion disk seen edge-on.

For this reason it would be extremely helpful to have a spectrum including the wavelength range around H-alpha. No precise measurements, nor a high signal-to-noise ratio are needed. The star TYC 1799 1159 1 is located at 3 39 33.8 +22 31 41 (J2000), about 2 degrees south-west of the Pleiades' centre (it is not a cluster member).

This request for a spectrum is a bit urgent, as the sun is now quickly approaching the star. We (the German association of variable-star observers, BAV) would like to use the forthcoming seasonal visibility break to plan the right follow-up observations and to set up observing proposals for the next season. For this, in turn, it would be extremely helpful to know whether there is a strong H-alpha emission line from the system.

Please report any results or other feedback to me via email to bastian@ari.uni-heidelberg.de

Kind regards, Uli Bastian
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Re: urgent observation request for TYC1799 1159 1

Postby jack martin » Fri Mar 12, 2021 5:33 pm

Ulrich,

Not sure TheSkyX would recognise TYC are there any other identifiers ?

Regards,

Jack

Essex UK
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Re: urgent observation request for TYC1799 1159 1

Postby Stu Todd » Sat Mar 13, 2021 3:25 am

A quick look in SIMBAD...


Identifiers (7) :

TYC 1799-1159-1
GSC 01799-01159
TIC 113982505
Gaia DR1 64628640645664512
EPIC 210971470
2MASS J03393386+2231402
Gaia DR2 64628644941989120
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Re: urgent observation request for TYC1799 1159 1

Postby Ulrich Bastian » Sun Mar 14, 2021 10:40 am

Many thanks to Stu Todd, this is the correct star.
Uli B.
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one spectrum received - Re: TYC1799 1159 1

Postby Ulrich Bastian » Sun Mar 14, 2021 11:21 am

Zurmuehl TYC1799 1159 1.png
Spectrum taken by Uwe Zurmuehl
Dear Forum members,

just now I received a spectrum from German amateur Uwe Zurmuehl, taken last night under difficult conditions. It looks like a normal K spectrum, with Na D, G band, H-alpha, -beta, -gamma in absorption, and no emission apparent. Uwe Zurmuehl commented that the run of the continuum (calibrated via a neighbouring A0 star) is consistent with an unreddened K2III star.

This quick and pleasant reaction has two consequences:
1) It takes the urgency out of my request. It answers my main question on the star perfectly and conclusively. Any even better spectrum would of course do no harm ;) , and a spectrum taken during the next eclipse minimum would be a gem. That minimum will be the last one to (possibly) be reachable before the seasonal break. It will occur on April 10, around 20:30 UT. It will not be observable from far northern latitudes, and generally from a fairly restricted range of longitudes only - if at all.
2) The astrophysical conundrum posed by the HRD location of the star and the characteristics of the eclipse lightcurves is confirmed, and kind of deepened even.

Kind regards, Uli Bastian
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Re: urgent observation request for TYC1799 1159 1

Postby Rainer Ehlert » Wed Mar 17, 2021 5:59 pm

Hi Ulrich,

I managed to get TYC 1799-1159-1 yesterday night and made 15 images each 450s and processed the outcome into a spectrum. I tried to calibrate the spectra with the instrument response curve I have. Nor perfect but trying to learn more and more with time. Just started again with Spectroscopy so please excuse mein stümperhafter Versuch :o

Unfortunately my sky is not that good anymore. Below the result. If it helps and you need more info I can provide it to you. Just tell me what you need and I will galdly send it to you.

Grüße Rainer


TYC_1799-1159-1_450s_LISA_600mm-0015_C_CC_HT2x_16bit_et_20210316.jpg
Last edited by Rainer Ehlert on Thu Mar 25, 2021 6:43 pm, edited 1 time in total.
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
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Re: urgent observation request for TYC1799 1159 1

Postby Ulrich Bastian » Wed Mar 17, 2021 7:59 pm

Dear Rainer, (and dear community)

yes, this spectrum helps me, like the one by Uwe Zurmuehl posted further up, and like a third one that Keith Shank (Texas, USA) mailed to me directly. All three convincingly and conclusively say that the strong H-alpha emission line that I hypothesized does not exist. The spectrum looks very much like that of a normal K giant in the red-giant clump (i.e. with central He burning ongoing), as the Gaia DR3 parallax and photometry suggested. This means that the 0.4-magnitude eclipses are not reated by some small H-alpha emitting object covered by the giant (this was my hypothetical way out of the astrophysical dilemma posed by the system), but that indeed something big must be covering 40 percent of the giant. Every 35 days for just an hour or so. Don't ask me what that could be. This exactly is the problem.

My next thought then is: Whatever that object may be, given its size it is improbable to have small mass. If it is massive indeed, it should create considerable radial-velocity variations on the giant star. Could not easily be less than 100 km/s.

Thus my next question to the community (and to Uwe Zurmuehl and Rainer in particular): What's the precision (and calibration reliability) of radial-velocity (RV) measurements that you can get out of your spectra? Potentially, the RV of the giant might vary by more than 100 km/s over the next 8 days. Any chance to get that??

The eclipse was on March 6, the period is 35 days. That is, on March 16 the RV will be maximally positive, around March 25 it will be zero again, on April 3 it will be maximally negative, and on April 10 there will be the next eclipse - again with about zero RV. That's for sure. The question is the amplitude. If we get that, we will immediately know the mass of the occulter - since the mass of a clump giant must be in a limited range, and the period is known.

I still find it amazing that I got a spectrum almost within hours, and now it's already three within a few days ...

Kind regards, Uli
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Re: urgent observation request for TYC1799 1159 1

Postby Ulrich Bastian » Wed Mar 17, 2021 8:36 pm

Ah, sorry,
I mixed up the signs! Of course the RV should now be negative, and it should be positive in early April, not vice versa.
Uli
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Re: urgent observation request for TYC1799 1159 1

Postby Rainer Ehlert » Wed Mar 17, 2021 10:00 pm

Thus my next question to the community (and to Uwe Zurmuehl and Rainer in particular): What's the precision (and calibration reliability) of radial-velocity (RV) measurements that you can get out of your spectra? Potentially, the RV of the giant might vary by more than 100 km/s over the next 8 days. Any chance to get that??


Hi Ulrich,

Nice to hear it was of use for you.

Now in regard to your above question I ahve to damit that I have no idea how to do that. If you would care to explain this to me via e-mail or perhaps a messenger chat ?

I can shoot the star today again and the next days provided there are no clouds an make more spectra. I think I will also need to shoot a reference star near TYC 1799-1159-1 for calibration purposes. I just saw today the Moon is 11° away from TYC 1799 ...

Hopefully the sky gets a bit better and so I get less sky light pollution. This has gone terrible compared to two years ago.

Will let you know how my image acquisition goes.

Grüße Rainer
regards Rainer____Observatorio Real de 14_____MÉXICO_____N 22° W 101°
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Re: urgent observation request for TYC1799 1159 1

Postby Robin Leadbeater » Thu Mar 18, 2021 12:07 am

Rainer Ehlert wrote:
Thus my next question to the community (and to Uwe Zurmuehl and Rainer in particular): What's the precision (and calibration reliability) of radial-velocity (RV) measurements that you can get out of your spectra? Potentially, the RV of the giant might vary by more than 100 km/s over the next 8 days. Any chance to get that??


Hi Ulrich,

Nice to hear it was of use for you.

Now in regard to your above question I ahve to damit that I have no idea how to do that. If you would care to explain this to me via e-mail or perhaps a messenger chat ?

I can shoot the star today again and the next days provided there are no clouds an make more spectra. I think I will also need to shoot a reference star near TYC 1799-1159-1 for calibration purposes. I just saw today the Moon is 11° away from TYC 1799 ...

Hopefully the sky gets a bit better and so I get less sky light pollution. This has gone terrible compared to two years ago.

Will let you know how my image acquisition goes.

Grüße Rainer


Hi Rainer,

I recommend reading the presentation "Observing with a LISA spectrograph - David Boyd" on the BAA website here
https://www.britastro.org/downloads/15701
slide 43-52

With care and good technique it is possible to get a radial velocity precision of better than 10km/s with the LISA and this G star is a good target for the cross correlation method. A good instrument response is not needed for radial velocity measurements as you are only interested in the position of the lines but you do need good low noise spectra and it is important to take calibration lamp spectra often. You should also take a spectrum of a bright star with a known radial velocity as a standard to get an absolute calibration.

Cheers
Robin
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