Mon, 07/15/2024 - 16:56
Hi All,
I captured a TrES-2b transit on JD2460504. (AAVSO report submitted, observer code IGE).
I see other observers (NANF, RHEC, TSAD, MBEB) have completed transit observations recently. My report and NANF's report for JD2460504 both show a Tc that significantly differs from the predicted Tc: our reports are "early" by about 50 -70 minutes (BJDtdb). The reported uncertainty for Tc in the Swarthmore transit database is +/- 32 minutes.
Anyone else seeing a similar difference in recent TrES-2 b transits and if so, any insights on what is going on?
Thanks,
George
George, what is happening is that on the Swarthmore transit site under Target List, the ExoPlanet Watch target database has not been updated in a couple of years. The Tmid prediction from it will give you a different Tmid prediction than if you select the NASA Exoplanet Archive database, which is updated more often.
For instance, on our observation on July 12, the Exoplanet Watch data base gives a Tmid at 07:06 UTC, +/- 32 minutes, while the NASA Exoplanet Archive gives a Tmid of 06:12 UTC, +/- 0 minutes.
The ExoPlanet Watch team is aware that the Swarthmore database is out of date.
However, the best way is to use the hot link for the Exoplanet Archive that shows up when Swarthmore generates the target list for your night/location. It will take you directly to their page which gives you the most current stellar parameters, exoplanet parameters, and has a transit predictor link that will give you the most current and most accurate Tmid prediction. In this case, it was 06:16 UTC.
So, my target selection starts with the EpW data base, because they have ranked targets in priority of importance, with the lower number indicating higher priority. It also gives me an idea of where that target will be from my location, and only a rough idea about the timing of my observation to get the Tmid sort of in the middle of a good light curve. I take note of the duration, also.
Then I just hit the Exoplanet Archive hot link, check the parameters there, and use their predictor.
The difference in observed Tmids, depending on how old the prediction data is really shows the necessity of keeping them fresh.
Hope this helps!
Anthony
Thanks, Anthony! By the way, is your AAVSO observer code NANF?
George
It is. This is a lot of fun!
Oh, and also what is happening is that this shows the importance of someone with a telescope actually laying eyes on these targets and updating the ephemeris, because, as you can see, the prediction you used to plan your observation was stale, and you got a Tmid that was multiple minutes off from what you expected. Imagine if you had submitted a proposal for time on a big scope and got a couple of hours six months from now. It would be a bit disappointing, not to mention expensive and possibly career delaying, to find out that half your scope time was wasted because the exoplanet was not in the place it was predicted to be.
Fortunately, however, in this case, the prediction data had been updated. You just didn't know it. Regardless, you got the data, and it will be reprocessed with the most current parameters, and the result of your work will still be valid and potentially useful, and your next one will be on target!
It's still amazes me that as amateurs, we can contribute this way.
I agree with you, Anthony, contribution to the science is another satisfying aspect to an already beautiful hobby.
Regarding the data we collect, is there a "campaign" mechanism in place for exoplanet transits, similar to variable star observations? I know that Exoplanet Watch recommends targets by region, but it seems to me that coordination among a group of serious observers would have benefits in data collection and afford learning opportunities to participants.
Maybe such coordination already exists?
George
Hi…
This is pretty Unusual
Hi Guys,
All the exoplanets in the NASA archive which are available from the public Swarthmore Transit Finder, are well-known with extensive transit observations reported. The ephemera’s have been refined and updated over a multi-year period. It was last modified in ExoFOP on 2023-03-24 and currently lists with a period of 2.471 days. Does that correspond with the period you worked with from the Transit Finder?
It’s very odd that you’d stumble onto a ‘confirmed exoplanet’ that made it into the NASA Archive and where Tc was off. I can’t help but wonder whether this might be an additional planet orbiting TrES 2, or whether something has transpired in the system that altered the orbit - unlikely but possible. You might want to check in with Dennis Conti, our AAVSO Exoplanet Section Leader.
Gary
Gary,
It would be exciting to have detected an additional planet around TrES-2, but I suspect the explanation is more mundane.
I obtained the transit times for the JD2460504 transit of TrES-2 from the Swarthmore web site, but I selected the "Exoplanet Watch" option rather than the NASA archive in the four radio buttons at the top of the web page. As Anthony pointed out in an earlier posting to this thread, the Watch option presents transit times that don't match the NASA archive.
I used the Transit Timing Service (exoplanetarchive.ipac.caltech.edu/cgi-bin/TransitView/nph-visibletbls?dataset=transits) to determine the Tc = 2460504.7611111 UT for this event. Converting this to BJDtdb for TrES-2 at my observatory location resulted in 10504.7638. The "Exoplanet Watch" option in Swarthmore reports Tc= 10504.7983 BJDtdb for this event, almost 54 minutes later than the NASA archive predicted Tc = 10504.7610. My observation, modeled using AIJ, indicates Tc=10504.7600.
This isn't the only object/transit timing that shows a difference between my observation times and the Exoplanet Watch times. I may continue to use the Exoplanet Watch option for priority recommendations, but the NASA archive option and Transit Timing Service will be used to check my observed times against predicted.
George