J/MNRAS/422/2024 X-ray-age relation and exoplanet evaporation (Jackson+, 2012)
The coronal X-ray-age relation and its implications for the evaporation of
exoplanets.
Jackson A.P., Davis T.A., Wheatley P.J.
<Mon. Not. R. Astron. Soc. 422, 2024 (2012)>
=2012MNRAS.422.2024J 2012MNRAS.422.2024J
ADC_Keywords: Stars, late-type ; X-ray sources ; Photometry, UBV ; Planets
Keywords: stars: activity - stars: formation - stars: late-type -
planetary systems - X-rays: stars
Abstract:
We study the relationship between coronal X-ray emission and stellar
age for late-type stars, and the variation of this relationship with
spectral type. We select 717 stars from 13 open clusters and find that
the ratio of X-ray to bolometric luminosity during the saturated phase
of coronal emission decreases from 10-3.1 for late K-dwarfs to
10-4.3 for early F-type stars (across the range 0.29<(B-V)0<1.41).
Our determined saturation timescales vary between 107.6 and 108.3
years, though with no clear trend across the whole FGK range.
We apply our X-ray emission - age relations to the investigation of
the evaporation history of 121 known transiting exoplanets using a
simple energy -limited model of evaporation and taking into
consideration Roche lobe effects and different heating/evaporation
efficiencies. We confirm that a linear cut-off of the planet
distribution in the M2/R3 versus a-2 plane is an expected result
of population modification by evaporation and that the known
transiting exoplanets display such a cut-off. We find that for an
evaporation efficiency of 25 percent we expect around 1 in 5 of the
known transiting exoplanets to have lost >10 percent of their mass
since formation. In addition we provide estimates of the minimum
formation mass for which a planet could be expected to survive for
4Gyrs for a range of stellar and planetary parameters.
We emphasise the importance of the earliest periods of a planet's life
for its evaporation history with 75 percent expect to occur within the
first Gyr. This raises the possibility of using evaporation histories
to distinguish different migration mechanisms. For planets with
spin-orbit angles available from measurements of the
Rossiter-McLaughlin effect no difference is found between the
distributions of planets with misaligned orbits and those with aligned
orbits. This suggests that dynamical effects accounting for
misalignment occur early in the life of a planetary system, although
additional data is required to test this.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 95 717 Data for individual cluster stars
table3.dat 96 124 *Planet data
table4.dat 84 124 *Host star parameters
table5.dat 100 124 Predictions for mass lost by the planets
in our sample
refs.dat 75 62 References
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Note on table3.dat and table4.dat: Most original data are taken from the
Exoplanet Encyclopedia (www.exoplanet.eu) with any additional references
listed in column Ref.
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name SIMBAD identifier
25- 36 A12 --- Cluster Cluster name
38- 43 F6.1 pc Dist Distance to star/cluster
45 I1 --- f_Dist [1]? Hyades distance flag (1)
47- 53 A7 --- r_Dist Reference(s) for distance
55- 58 F4.2 [yr] log(Age) Log of age (base 10)
60- 66 A7 --- r_log(Age) Reference(s) for age
68- 72 F5.2 mag Vmag V magnitude
74- 77 F4.2 mag (B-V)0 De-reddened B-V colour index
79- 83 F5.2 [W] log(Lx) Log of X-ray luminosity (base 10)
85- 89 F5.2 [-] log(Lx/Lb) Log of bolometric-to-X-ray ratio
91- 95 A5 --- Ref Reference for X-ray and photometric data
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Note (1): Most Hyades have individual distances, those flagged were assigned
a default distance of 45pc, see Stern et al. (1995ApJ...448..683S 1995ApJ...448..683S).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Star Host star name
13 A1 --- Pl [b-g] Planet designation
16- 21 F6.3 Mjup MP Planet mass
23- 27 F5.3 Rjup RP Planet radius
29- 36 F8.4 d Per Orbital period
38- 43 F6.4 AU a Semi-major axis of planet orbit
45- 48 F4.2 --- ecc ? Eccentricity of planet orbit
50- 52 I3 deg |lam| ?=- Absolute spin-orbit misalignment angle
54- 59 F6.2 m/s2 gP Surface gravity (1)
61- 65 I5 kg/m3 rhoP Mean density (1)
67- 72 F6.4 AU Mean orbital distance (1)
74- 77 F4.2 --- 1/K(eps) Roche lobe mass loss enhancement factor
(1/K(ε) (1)
79- 83 F5.2 [J] log(-PE) Planetary binding energy (1)
85 A1 --- ref Reference, in refs.dat file
87- 96 A10 --- OName Other planet name
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Note (1): calculated directly from the basic planetary and/or host parameters.
See Sections 3.2 for the form of and K(eps) and 3.4.2 for PE, note
that the value for PE listed here does not include the Roche lobe
correction.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Star Star name
13- 16 F4.2 Msun Mass Star mass
18- 33 A16 --- SpType MK spectral type
34- 38 F5.3 --- B-V ? B-V colour index only when used for SpType (1)
40- 44 F5.2 mag Vmag ?=- V magnitude
46- 50 F5.2 mag mbol ?=- Bolometric magnitude (2)
52- 55 I4 pc Dist ?=- Distance
57- 60 F4.1 Gyr Age Age
61 A1 --- n_Age [+] Note for assumed age of 4Gyr (3)
63- 67 F5.2 [J] log(EX) Total X-ray energy emitted by the star (4)
68 A1 --- n_log(EX) [*] Note on log(EX) (5)
70- 75 A6 --- refS References
77- 84 A8 --- OSName Other star name
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Note (1): Where a B-V colour is listed, the corresponding spectral type has been
determined from the colour using the tables presented in Lang (1991).
Note (2): The bolometric magnitude is calculated from the V -band magnitude and
a bolometric correction based on the spectral type (also using the tables of
Lang 1991).
Note (3): +: No literature age is available for this star so an age of 4 Gyrs
is assumed.
Note (4): EX is the total X-ray energy emitted by the star over a period from
formation to its present age as calculated using our X-ray characteristics
for the appropriate spectral type as presented in Table 2 and described in
Sections 2.2.2 and 2.2.3.
Note (5): * : Vmag. or distance information is lacking for these stars and thus
EX was calculated using the bolometric luminosity of a typical star of the
same spectral type as the host (taken from the tables presented in Lang,
1991, Astrophysical Data: Planets and Stars. Springer-Verlag, New York).
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Star Host star name
13 A1 --- Pl [b-g] Planet designation
15- 20 F6.3 Mjup MP Planet mass
22- 28 F7.4 Mjup Mi1R Initial mass Mi in constant radius
approximation for η=1 (1)
30- 36 F7.4 Mjup Mi1d Initial mass Mi in constant density
approximation for η=1 (1)
38- 44 F7.4 Mjup Mi0.25R Initial mass Mi in constant radius
approximation for η=0.25 (1)
46- 52 F7.4 Mjup Mi0.25d Initial mass Mi in constant density
approximation for η=0.25 (1)
54- 61 F8.6 --- dM1R Fraction of initial mass lost β in
constant radius approximation for η=1
63- 70 F8.6 --- dM1r Fraction of initial mass lost β in
constant density approximation for η=1
72- 79 F8.6 --- dM0.25R Fraction of initial mass lost β in
constant radius approximation for η=0.25
81- 88 F8.6 --- dM0.25d Fraction of initial mass lost β with
constant density approximation for η=0.25
89 A1 --- Note [*] missing photometry or distance (2)
91-100 A10 --- OName Other planet designation
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Note (1): Initial masses with the fraction of the initial mass lost to reach
the present day mass, η being the efficiency factor.
See Sections 3.4.2 and 3.6 for further detail.
Note (2): *: V mag. or distance information is lacking for the hosts of these
planets and thus the predicted fractional mass losses were calculated using
the bolometric luminosity of a typical star of the same spectral type as the
host (taken from the tables presented in Lang, 1991, Astrophysical Data:
Planets and Stars. Springer-Verlag, New York).
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Ref Reference code
4- 22 A19 --- Bibcode Bibcode
24- 53 A30 --- Author Author's name
56- 75 A20 --- Com Comments
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Acknowledgements:
Alan Jackson, ajackson(at)ast.cam.ac.uk
(End) Alan Jackson [IoA, Cambridge, UK], Patricia Vannier [CDS] 27-Jan-2012