urgent observation request for TYC1799 1159 1

Re: urgent observation request for TYC1799 1159 1

Postby Rainer Ehlert » Thu Mar 18, 2021 2:10 am

Hi Robin,

Thsnk. Will do. BTW I have now a starter lamp integrated in the telescope cover and with this I can shoot calibration frames in every position. The same lamp was calibrated many years ago by Richard Walker when in some forum there was a opinion exchange about this starter lamps. In Europe the brand OSRAM but I do not get them here. My starter lamp has Argon and Krypton gas.

regards Rainer


Fulgore_Glimmlampe_2.jpg
Fulgore_Glimmlampe_2.jpg (397.8 KiB) Viewed 1560 times



Argon-Krypton_60s_LISA_600mm-0030_C_CC_HT3x0.25_DYB_img.jpg



Fulgore_Calibration_profile.jpg
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Re: urgent observation request for TYC1799 1159 1

Postby Rainer Ehlert » Thu Mar 18, 2021 7:00 pm

Hi Ulrich,

I was able to shot 13 images each 600 seconds but the last one were already quite low over the Horizon.

Below the graph. I labeled where the spectra has its lowest point. Also attached a fit file for your inspection. I just found out the forum does no accept the file type *.fit for upload.

Maybe we can exchange information adn you explain me better how to work our this file. I made a spectra of the nearby A0 star TYC 1799-660-1. Not yet processed. Also I made some calibration images of my calibration lamp and also not yet processed.

Appreciate your help.

regards Rainer


TYC_1799-1159-1_600s_LISA_625mm-0013_C_CC_HT2x_16bit_et_20210317.jpg
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Re: urgent observation request for TYC1799 1159 1

Postby Ulrich Bastian » Wed Mar 24, 2021 12:57 pm

Hallo Rainer,

sorry for replying so late. I was distracted by urgent work for the Gaia satellite mission. Excellent spectrum, thanks! I will carefully look at it tomorrow. As for the practical treatment of the spectra, I am not the expert to ask. I guess you can find more and better advice from others in the forum. Any volunteers out there? ;)

If not, then simply send me your spectrum by email (bastian@ari.uni-heidelberg.de), plus the calibrartuon lamp spectrum, and I will ask the Mexican colleagues (see my next message) whether they can do a wavelength calibration and RV determination on it. They have the software to do that.

Thanks again, Uli
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TYC1799 1159 1 - new hypothesis, new observational emphasis

Postby Ulrich Bastian » Wed Mar 24, 2021 1:19 pm

Dear all,

Klaus-Peter Schroeder from University of Guanajuato (Mexico) has proposed a new model hypothesis which might explain this mysterious system: The very high velocity of the occulting body needed to produce the short duration of the eclipses could be due to a very high eccentricity of the orbit, rather than due to very high masses involved. This idea would explain not only the short eclipses, but also avoid the assumption of exotic objects. It would also explain the very small uncertainty of the star's radial velocity in the Gaia catalogue. The mean error of .16 km/s implies that Gaia has not seen velocity variations over the first two mission years. With a circular orbit, this would be very surprising. With a high eccentricity, this may just be chance: Such a system would most of the time hover near the periastron, with little velocity changes occurring for most of the time. And Gaia observes all stars only sporadically, and at irregular time intervals. And the number of visits is especially small for sky areas close to the ecliptic!

However, this would make the system as a whole no less exotic than before. Such a high eccentricity with only 35 days of orbital period is nearly impossible dynamically with a clump giant in the system. Any originally existing eccentricity should have gone away during the previous phase when the star was high up on the giant branch. Prof. Schroeder offers a way out of this dilemma: The system might have come into this configuration only very recently. There are two possible paths that this might happen: The giant has recently caught the partner gravitationally, or a third body (star) has recently made a very close encounter with the - previously circular - system, disturbing the orbit into a high eccentricity. Great. No exotic objects any more, but one of two extremely rare events involved instead.

Why do I explain all this to you? Because this new idea shifts the observational emphasis: Now the biggest values (positive and negative) of radial velocity should no longer appear at 9 days before and after the eclipses, but during just two or three days on either side of the eclipses. The best chance to see large radial-velocity changes now concentrate on the narrow time range April 6-14.

The Mexican colleagues will try to activate their 1.2m telescope on the star during that time interval, but they are uncertain whether it can be done because then the zenith distance is already too large for the regular observation procedures of their telescope.

Best regards, Uli Bastian
Last edited by Ulrich Bastian on Sat Mar 27, 2021 6:00 pm, edited 2 times in total.
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Re: urgent observation request for TYC1799 1159 1

Postby Rainer Ehlert » Wed Mar 24, 2021 6:10 pm

Hallo Ulrich,

You will get an email from eastpier@.....com so it does not land in your SPAM folder

Grüße Rainer
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Re: urgent observation request for TYC1799 1159 1

Postby Robin Leadbeater » Fri Mar 26, 2021 2:06 am

Hi Ulrich

Here are four spectra covering 20210316-20210321 compared with Pickles K4iii as a reference. (open the image in a new tab to see it in correct scale)

tyc1799-1159-1_20210316-20210321_Leadbeater.png
tyc1799-1159-1_20210316-20210321_Leadbeater.png (100.2 KiB) Viewed 1455 times



There are Radial Velocities for three of the spectra, measured by cross correlation with spectra of iota Aur recorded the same nights. I do not have enough data to measure the uncertainty in RV but I would guess it to be ~20km/s 1 sigma so the differences between the nights may not be significant. The spectra can be accessed from the BAA spectroscopy database
https://britastro.org/specdb/

It is too low for me now and will not be visible for me again until August I am afraid

Cheers
Robin
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Re: urgent observation request for TYC1799 1159 1

Postby Ulrich Bastian » Sat Mar 27, 2021 5:58 pm

Thanks a lot to Rainer Ehlert and to Robin Leadbeater for additional data. They nicely confirm what we think to know about the star (spectral type, luminosity class, rough metallicity from the other spectra, and absolute magnitude from Gaia parallax). This is reassuring. Robin's RVs may be inconclusive at the moment, but let's wait and see what else comes in. I am fully aware how difficult it is to get good RV calibrations (i.e. better than 0.01 percent wavelength calibrations).

I will keep both the observers (directly via email) and the forum updated of new developments.

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

Postby Ulrich Bastian » Wed Mar 31, 2021 5:10 pm

Dear all,
our professional spectroscopic friends from Mexico (see my post of March 24) have succeeded to collect 6 spectra in 9 nights with their 1.2m telescope and fiber-coupled spectrograph. Over about one quarter of the orbital period the radial velocity stayed stubbornly at +56 km/s (the value that also Gaia has measured about three years earlier), with no trend at all and with an observational scatter well below 1 km/s. This means that the huge orbiting and eclipsing "something" does not have a stellar mass.
This kills the last idea we had to explain the system without some very exotic ingredients (namely the idea of a big star on an extremely eccentric orbit, see March 24). What remains is the idea of a freshly torn hot Jupiter (or so), i.e. the debris cloud of a planet that was destroyed some time last year by a collision or by tidal forces from the giant star. This idea arose back in January already, when a check in sky surveys showed no eclipses before October 2020. The idea was fostered when in March I noticed that the March 6 eclipse was twice as long as the Nov 21 eclipse. This fact nicely fits with an expanding/dispersing debris cloud.
But I/we did not wish to ventilate this idea as long as there were any alternatives - in order not to ridicule ourselves or appear in the yellow press. Even now it is just a remote possibility, but the only one that fits all observations.
Anyway, no further spectroscopy is needed for the time being. The next eclipse (April 10) is the last one before the seasonal break. The sun is already so close to the star, and the eclipse is at such an inconvenient UT that the only places where it could reasonably be observed are in the middle of the Atlantic ocean. When the star reappears from the glare of the sun (in August) it will be the job of the lightcurve people (photometrists) to see whether it still shows noticeable eclipses - or whether perhaps the cloud has meanwhile dispersed completely.

Your spectra were extremely helpful, for several aspects. They confirmed the nature of the star (which previously had only been inferred from the Gaia photometry and parallax), they refuted the possibility of a huge H-alpha emission from an accretion disk, and - most of all - they helped motivate the Mexican professionals to do the high-precision radial velocities.

I will inform you as soon as the post-break photometry (from August onwards) gives reason for further spectroscopy. And even if not: I will anyway at some time inform you of the outcome of this strange astrophysical conundrum.

Many, many thanks again, and kind regards to the entire forum,
Uli Bastian
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