J/A+A/634/A29 Kepler-278 and Kepler-391 spectra (Jofre+, 2020)
Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting
planets. I. Detailed characterization of the multi-planet systems Kepler-278
and Kepler-391.
Jofre E., Almenara J., Petrucci R., Diaz R.F., Gomez Maqueo Y., Martioli E.
Ramirez I., Garcia L., Saffe C., Canul E.F., Buccino A., Gomez M.,
Moreno Hilario E.
<Astron. Astrophys. 634, A29 (2020)>
=2020A&A...634A..29J 2020A&A...634A..29J (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Spectra, optical
Keywords: stars: fundamental parameters - stars: abundances -
stars: individual: Kepler-278, Kepler-391 - planetary systems -
techniques: spectroscopic - stars: individual: Kepler-391
Abstract:
Kepler-278 and Kepler-391 are two of the three evolved stars on the
red giant branch (RGB) known to date, to host multiple short-period
transiting planets. Moreover, these planets are among the smallest
discovered around RGB stars. Here, we present a detailed stellar and
planetary characterization of these remarkable systems. Methods. Based
on high-quality spectra from Gemini-GRACES of Kepler-278 and
Kepler-391, we obtained refined stellar parameters and precise
chemical abundances of 25 elements. Nine of these elements and the
carbon isotopic ratios, 12C/13C, were not previously measured.
Also, combining our new stellar parameters with a photodynamical
analysis of the Kepler light curves, we determined accurate planetary
properties of both systems. Results. Our revised stellar parameters
agree reasonably well with most of the previous results, although we
find that Kepler-278 is ∼15% less massive than previously reported.
The abundances of C, N, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn,
Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, and Ce, in both stars, are consistent
with those of evolved nearby thin disk stars. Kepler-391 presents a
relatively high abundance of lithium (A(Li)NLTE=1.29±0.09dex),
which is likely a remnant from the main-sequence phase. The precise
spectroscopic parameters of Kepler-278 and Kepler-391 along with their
high 12 C/13 C ratios show that both stars are just starting their
ascent on the RGB. The planets Kepler-278b, Kepler-278c, and
Kepler-391c are warm sub-Neptunes, whilst Kepler-391b is a hot
sub-Neptune that falls in the Hot Super-Earth desert and therefore it
might be undergoing photo-evaporation of its outer envelope. The
high-precision obtained in the transit times allowed us not only to
confirm Kepler-278c's TTV signal but also to find evidence of a
previously undetected TTV signal for the inner planet Kepler-278b.
From the presence of gravitational interaction between these bodies we
constrain, for the first time, the mass of Kepler-278b (Mp=56MEarth)
and Kepler-278c (Mp=35MEarth). The mass limits, coupled with our
precise determinations of the planetary radii, suggest that their bulk
compositions are consistent with a significant amount of water content
and the presence of H2 gaseous envelopes. Finally, our photodynamical
analysis also shows that the orbits of both planets around Kepler-278
are highly eccentric (e∼0.7) and, surprisingly, coplanar. Further
observations (e.g., precise radial velocities) of this system are
needed to confirm the eccentricity values presented here.
Description:
Gemini-GRACES reduced spectra as FITS files of the stars Kepler-278 and
Kepler-391.
Objects:
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RA (2000) DE Designation(s)
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19 20 25.72 +38 42 08.0 Kepler-278 = KIC 3640905
19 22 29.23 +51 03 26.3 Kepler-391 = KIC 12306058
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
spectra.dat 103 2 List of fits spectra
fits/* . 2 Individual fits spectra
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Byte-by-byte Description of file: spectra.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Star name
12- 13 I2 h RAh Right ascension (J2000)
15- 16 I2 min RAm Right ascension (J2000)
18- 22 F5.2 s RAs Right ascension (J2000)
24 A1 --- DE- Declination sign (J2000)
25- 26 I2 deg DEd Declination (J2000)
28- 29 I2 arcmin DEm Declination (J2000)
31- 35 F5.2 arcsec DEs Declination (J2000)
37- 42 I6 --- Nx Number of pixels along X-axis
44- 53 A10 "datime" Obs.date Observation date
55- 58 I4 0.1nm blambda Lower value of wavelength interval
60- 63 I4 0.1nm Blambda Upper value of wavelength interval
65- 67 I3 Kibyte size Size of FITS file
69- 83 A15 --- FileName Name of FITS file, in subdirectory fits
85-103 A19 --- Title Title of the file
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Acknowledgements:
Emiliano Jofre, emiliano(at)astro.unam.mx
(End) Patricia Vannier [CDS] 22-Dec-2019