Kepler stellar properties study

• by ajamyajax

  Check this out, looks like there is a fairly good correlation between the 2MASS color delta values and stellar mass and radius. This data only from the Kepler confirmed planets list, but I think we could use these ranges to better estimate the stellar properties of our K2 candidates. Best Regards, Mark

  
  

  Here is the data as charted above:

  Kepler Name, Stellar mass, Stellar radius, Morgan-Keenan classification, J - H, H - K
  

  Kepler-412 1.17 1.29 G3 V 0.258 0.095
  
  Kepler-117 1.13 1.61 F8 V 0.336 -0.023
  
  Kepler-138 0.57 0.53 M1 V 0.613 0.174
  
  Kepler-420 0.99 1.13 G5 V 0.395 0.101
  
  Kepler-421 0.79 0.76 G9/K0 0.39 0.084
  
  Kepler-423 0.85 0.95 G4 V 0.295 0.068
  
  Kepler-425 0.93 0.86 K1 V 0.445 0.125
  
  Kepler-426 0.91 0.92 G1 V 0.394 0.018
  
  Kepler-427 0.96 1.35 G2 V 0.347 0.037
  
  Kepler-428 0.87 0.80 K1 V 0.472 0.061
  
  Kepler-444 0.76 0.75 K 0.472 0.069
  
  Kepler-445 0.18 0.21 M4 0.613 0.319
  
  Kepler-446 0.22 0.24 M4 0.516 0.248
  
  Kepler-447 1.00 1.05 G8 V 0.332 0.073
  
  Kepler-91 1.31 6.30 K3 0.555 0.099
  
  Kepler-101 1.17 1.56 G3 IV 0.291 0.101
  
  Kepler-17 1.16 1.05 G2 V 0.322 0.085
  
  Kepler-21 1.34 1.86 F6 IV 0.198 0.086
  
  Kepler-22 0.97 0.98 G5 V 0.312 0.059
  
  Kepler-32 0.54 0.53 M1 V 0.715 0.144
  
  Kepler-38 0.94 1.75 G4 V 0.318 0.07
  
  Kepler-39 1.29 1.40 F7 V 0.237 0.081
  
  Kepler-40 1.48 2.13 F5 IV 0.242 0.024
  
  Kepler-41 1.15 1.29 G2 V 0.324 0.046
  
  Kepler-42 0.13 0.17 M 0.492 0.22
  
  Kepler-43 1.27 1.38 F8 V 0.253 0.056
  
  Kepler-44 1.12 1.35 G2 IV 0.371 0.091
  
  Kepler-45 0.59 0.55 M 0.672 0.185
  
  Kepler-61 0.64 0.62 K7 V 0.652 0.154
  
  Kepler-62 0.69 0.64 K2 V 0.517 0.08
  
  Kepler-66 1.04 0.97 G0 V 0.332 0.068
  
  Kepler-67 0.86 0.78 G9 V 0.4 0.186
  
  Kepler-69 0.81 0.93 G4 V 0.347 0.05
  
  Kepler-74 1.18 1.12 F8 V 0.298 0.05
  
  Kepler-75 0.91 0.89 K0 V 0.403 0.144
  
  Kepler-76 1.20 1.32 F 0.209 0.042
  
  Kepler-77 0.95 0.99 G5 V 0.314 0.083
  
  Kepler-78 0.76 0.74 G 0.509 0.089
  
  Kepler-186 0.54 0.52 M1 0.649 0.219
  

  Data Credit: NASA Exoplanet Archive which is operated by the California Institute of Technology
  

  Update: here are each of the classes in this confirmed data plotted separately:

  
  
  
  

  Posted May 8, 2015 2:57 PM

• by zoo3hans

  Thanks Mark, quite useful indeed.

  Posted May 8, 2015 7:16 PM

• by ajamyajax

  Also looks like the KOI tables values have a similar correlation overall. The radii greater than ~1.5 and J - H values greater than ~0.37 stars are an interesting partial exception however because they are also "low mass" in the KOI table.

  

  Posted May 10, 2015 5:27 PM

• by ajamyajax

  And this is interesting as well, the Fe/H ratio appears to have a somewhat inverse correlation with the J - H color and mass or radius values. Will need to follow up these mini-studies with some paper research sometime.

  

  Posted May 10, 2015 5:29 PM

• by Shellface

  (Still not really here - now because "oh god exams". Won't be back properly until, like, July (dagnabbit))

  Good to see others picking up on the use of colours, and that sort of thing. What I have been using as reference is this file, which has various colour indices across most spectral types and effective temperatures, and reference masses. I would recommend using it wherever possible in future.

  Also, the 2MASS point source catalogue can be accessed through here, which gives JHK colours for most (if not all) stars that Kepler can study. Note that the input doesn't like plus signs in the declination, for some reason.

  Concerning the KIC parameters, I am aware that the derived temperatures are accurate, but the metallicities and surface gravities are not, to the extent where the latter two are uncorrelated with values determined by spectroscopy. I expect the correlation between metallicity and colour represents biasing/systematics in the KIC modelling, as it would have no physically sensible explanation.

  Regardless, metallicity has fairly little effect on the other stellar parameters for typical values (though metallicity certainly has significant effects at extreme values). As density, and thus surface gravity, can be derived from transit parameters, I believe that colour information should only really be used for spectral typing by anyone not armed with actual stellar models, accurate or not.

  Anyway, let's see you folks doing colour analyses routinely! I'm totally not trying to save my energy, har har.

  (and, aja - I think referring to stellar parameters by "ratio", though not incorrect, sounds a bit awkward. I've never seen it used anywhere else, so I must suggest you use the regular term of "…in units of solar mass/radii/etc.")

  Posted May 10, 2015 6:22 PM

• by ajamyajax in response to Shellface's comment.

  SF: thank you for the data link which is quite useful also. I wrote a few programs to work with it, and will post some K2 stellar estimates later using them. Your analysis is more thorough of course, so feel free to correct/refine any of these also later when you have the time. FWIW, I did run a quick comparison of mass values in the KOI tables vs. the mass estimates in the data file using Teff, J-H, and H-K values in order below here. And it seems that Teff was more accurate in predicting the stellar mass or at least more consistent in this small dataset test.

  Kepler ID, Stellar mass, Stellar radius, Kep Mag, J - H, H - K, Teff, (spectral type and mass ests)
  
  7447200 0.5500 0.5300 13.822 0.543 0.136 3914.00 ('K9V', 0.6) ('K3V', 0.81) ('K6V', 0.7)
  
  6949607 0.5900 0.5700 15.036 0.567 0.048 4072.00 ('K7V', 0.64) ('K6V', 0.7) ('F1V', 1.5)
  
  10905746 0.3230 0.3160 13.496 0.669 0.175 3545.00 ('M2V', 0.5) ('M7V', 0.098) ('K7V', 0.64)
  
  11923270 0.5100 0.4900 15.937 0.661 0.185 3672.00 ('M1V', 0.52) ('M7V', 0.098) ('K8V', 0.62)
  
  7603200 0.5200 0.5000 12.925 0.613 0.174 3841.00 ('M0V', 0.58) ('K6V', 0.7) ('K7V', 0.64)
  
  7907423 0.4400 0.4200 15.234 0.686 0.184 3568.00 ('M2V', 0.5) ('M8V', 0.082) ('K8V', 0.62)
  
  4832837 0.5800 0.5600 14.915 0.624 0.122 3941.00 ('K8V', 0.62) ('K7V', 0.64) ('K3V', 0.81)
  
  9575728 0.5510 0.5420 14.137 0.68 0.141 3901.00 ('K9V', 0.6) ('M9V', 0.065) ('K5V', 0.75)
  
  4249725 0.5900 0.5700 14.735 0.601 0.111 4096.00 ('K7V', 0.64) ('K5V', 0.75) ('K4V', 0.78)
  

  Spectral type credit and reference per Eric Mamajek's comment in the link file:

  "Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars"

  Mark J. Pecaut, Eric E. Mamajek

  http://arxiv.org/abs/1307.2657

  Posted May 15, 2015 7:55 PM

• by ajamyajax

  And this curve will just confirm the obvious for experienced planet hunters, but there is a nice correlation as seen here with Teff and mass/radius in the confirmed planets data:

  Credit and Reference:

  http://www.astro.keele.ac.uk/jkt/tepcat/

  John Southworth - Lecturer in Astrophysics - Keele University, UK

  

  Posted June 4, 2015 8:27 PM

• by ajamyajax

  Correction/just busy: will compare K2 data later but just based on a sample population of KOI tables values, maybe we can identify smaller M-dwarfs if a Kepmag - K color > 2.5 or so.

  

  Posted June 6, 2015 3:04 PM

• by ajamyajax in response to ajamyajax's comment.

  FWIW here are the delta magnitude values for some of the C2 targets we have looked at recently:

  epic_number,k2_campaign,ra,dec,tm_name,k2_jmag,k2_hmag,k2_kmag,k2_kepmag,(k2_kepmag-k2_kmag)
  

  204506777,241.824112,-22.060158,2MASS J16071778-2203364,7.543,7.146,7.047,8.752 ,1.705
  
  203771098,242.573715,-24.990332,2MASS J16101770-2459251,9.635,9.294,9.180,11.648 ,2.468
  
  203826436,243.451004,-24.787062,2MASS J16134824-2447132,10.692,10.214,10.142,12.241 ,2.099
  
  205071984,252.426086,-19.542822,2MASS J16494226-1932340,10.404,9.993,9.821,12.005 ,2.184
  
  202675839,243.842102,-28.780161,2MASS J16152210-2846485,10.929,10.598,10.490,12.362 ,1.872
  
  203865172,253.455399,-24.635683,2MASS J16534928-2438083,9.612,9.316,9.236,10.673 ,1.437
  
  202688980,244.220779,-28.730322,2MASS J16165298-2843493,10.588,10.308,10.232,11.772 ,1.54
  
  202834934,250.766891,-28.191156,2MASS J16430404-2811279,13.020,12.277,12.125,15.385 ,3.26
  
  202710713,244.066895,-28.649134,2MASS J16161605-2838569,9.521,8.664,8.366,12.237 ,3.871
  
  202821899,249.160019,-28.239061,2MASS J16363840-2814205,11.286,10.902,10.805,12.577 ,1.772
  
  202900527,246.811157,-27.957048,2MASS J16271467-2757252,10.686,10.225,10.030,12.303 ,2.273
  
  203753577,252.861847,-25.053404,2MASS J16512684-2503124,9.811,9.562,9.477,11.106 ,1.629
  
  203776696,246.611420,-24.969948,2MASS J16262672-2458119,12.729,12.126,11.853,15.037 ,3.184
  

  Data Credit: NASA Exoplanet Archive which is operated by the California Institute of Technology
  

  Posted June 8, 2015 7:42 PM

• by ajamyajax

  And also looks like there is a nice correlation with stellar surface gravity (log g) and stellar radii in the confirmed planet data. Saw some RAVE data available for these values because of a recent Shellface post (thanks again). And only the main population of data shown in this close-up to illustrate the trend here.

  

  Data Credit: NASA Exoplanet Archive which is operated by the California Institute of Technology
  

  Posted October 27, 2015 3:08 PM

• by ajamyajax in response to ajamyajax's comment.

  Thought it might be useful to estimate surface gravity for our work here, so I used the 'flicker' technique discussed in this paper as a guide and wrote a program:

  "Flicker as a tool for characterizing planets through Asterodensity Profiling"

  David M. Kipping, Fabienne A. Bastien, Keivan G. Stassun, William J. Chaplin, Daniel Huber, Lars A. Buchhave

  http://arxiv.org/abs/1403.5264

  For the most part, my tests are fairly close to published results even though they are just estimates. So hopefully, combined with other tools I think these will help with the stellar radius calculations I post here.

  ** K1 log(g) **
  

  9955598: mine 4.66; s/b 4.5
  
  10864656: mine 3.40; s/b 3.35
  
  3548044: mine 4.34; s/b 4.39
  
  4570949: mine 4.23; s/b 4.20
  
  11551692: mine 4.53; s/b 4.54
  
  9478990: mine 4.49; s/b 4.40
  
  8077137: mine 4.03; s/b 4.07
  
  9881662: mine 4.14; s/b 4.27
  

  ** K2 log(g) **
  

  203826436: mine 4.6; s/b 4.66
  
  202675839: mine 4.34; s/b 4.25
  
  202088212: mine 4.3; s/b 4.37
  
  201577035: mine 4.52; s/b 4.53
  
  201384232: mine 4.59; s/b 4.67
  
  203771098: mine 4.43; s/b 4.29
  
  206247743: mine 3.42; s/b 3.60
  
  204129699: mine 4.65; s/b 4.60
  

  Note published results from the NASA Exoplanet Archive and:

  "PLANETARY CANDIDATES FROM THE FIRST YEAR OF THE K2 MISSION"

  http://arxiv.org/pdf/1511.07820v1.pdf

  Posted November 27, 2015 4:51 PM