EPIC 202091388 - 4 transits

by JKD

http://talk.planethunters.org/#/subjects/APH0000auv?quarter=0-1

Posted December 10, 2014 7:09 PM

by Dolorous_Edd

Target is listed under GO0111_LC

GO0111 Sanchis Ojeda DETECTION OF EARTH-SIZE PLANETS USING K2

enter image description here

N | Cat | ID/Name | RA/Lon | Dec/Lat | X | Y

1 | http://archive.stsci.edu/k2/epic/search.php | 202091388 | 91.3638| 21.2560| 150.0| 150.0

2 | http://archive.stsci.edu/k2/epic/search.php | 208517193 | 91.3651| 21.2508| 127.5| 55.8

3 | http://archive.stsci.edu/k2/epic/search.php | 208518360 | 91.3724| 21.2554| 6.2| 139.2

4 | http://archive.stsci.edu/k2/epic/search.php | 208520560 | 91.3721| 21.2642| 10.1| 296.1

5 | http://archive.stsci.edu/k2/epic/search.php | 208520602 | 91.3549| 21.2643| 298.6| 298.8

Posted December 10, 2014 7:12 PM

by Dolorous_Edd

https://www.cfa.harvard.edu/~avanderb/k2c0/ep202091388.html

Posted December 10, 2014 9:35 PM

by Shellface

One star in-aperture, mid-G colours, dwarf-implying transit length. Transit depth of ~0.12% implies a companion radius of ~3 Rearth, if my maths is right. Seems like a valid small candidate!

Posted December 10, 2014 10:20 PM

by ajamyajax

EPIC 202091388: just a few charts to add to this low drop in flux candidate. At a glance looks like a bgeb maybe, however only a few data pts make the difference in my odd/even plot anyway. And the two somewhat similar transits shown here are consecutive. Also 3Re would be a nice to see in this data (vs all those HJs).

s1=1940.387 p1=6.477 d1=0.15 (3.6 hours)

Posted January 3, 2015 1:12 AM

by Shellface

Ah yes, forgot about this one. Better treatment of the star's colours maintain a spectral type of ~G5. There's no indication for any other stars in the Kepler aperture, so there's probably no blending.

The transit length suggests a dwarf host, as does the rather noticeable modulation of the lightcurve, which is probably due to spots. The rotational period is about 8.8 days, which indicates a young star (I'm not much of one for gyrochronology, but that's perhaps 0.5 - 1 Gyr). This makes it perhaps somewhat unsuitable for RV observations, moreso when considering its Kepmag = 13.5. However, the transits correspond to a companion radius of ~3.3 Rearth, so the expected companion mass is about 1 Neptune mass (17-and-a-bit earths). This would result in an RV semi-amplitude of around 5 m/s, which is perhaps twice as large as the RV variation due to spots. Due to their similar periods it would take at least a few orbital periods to disentangle the signals, but this is still manageable. Good low-mass candidate.

As an aside, for a Kepmag = 13.5 star, the expected photometric precision is ~150 ppm (i.e 0.00015 mag). Thus the transits have a S/N of about 7, and the odd/even transits have the same depth to 1-2σ. For such shallow K2 transits, I expect odd/even diagrams won't be useful unless the star is extremely bright.

Also 3Re would be a nice to see in this data (vs all those HJs).

Mm, gotta agree. It's just the smaths of the situation make it a lot harder to identify shallow events with K2 data, compared to K1 stars of the same character. PH probably won't find too many small planets with K2.

Posted January 3, 2015 2:40 AM

by Dolorous_Edd

Here is Keppixseries for 202091388 around pixel with coord Column= 209 , Row = 470

enter image description here