J/AJ/168/177 Detecting exoplanet transits: X-ray informations (Cilley+, 2024)
Detecting exoplanet transits with the next generation of X-ray telescopes.
Cilley R., King G.W., Corrales L.
<Astron. J., 168, 177 (2024)>
=2024AJ....168..177C 2024AJ....168..177C
ADC_Keywords: Exoplanets ; Space observations ; X-ray sources ; Photometry
Keywords: X-ray astronomy ; Exoplanets
Abstract:
Detecting exoplanet transits at X-ray wavelengths would provide a
window into the effects of high-energy irradiation on the upper
atmospheres of planets. However, stars are relatively dim in the
X-ray, making exoplanet transit detections difficult with current
X-ray telescopes. To date, only one exoplanet (HD 189733 b) has an
X-ray transit detection. In this study, we investigate the capability
of future X-ray observatories to detect more exoplanet transits,
focusing on both the NewAthena Wide Field Imager instrument and the
proposed Advanced X-ray Imaging Satellite (AXIS), which provide more
light-collecting power than current instruments. We examined all the
transiting exoplanet systems in the NASA Exoplanet Archive and
gathered X-ray flux measurements or estimates for each host star. We
then predicted the stellar count rates for both AXIS and NewAthena and
simulated light curves, using null-hypothesis testing to identify the
top 15 transiting planets ranked by potential detection significance.
We also evaluate transit detection probabilities when the apparent
X-ray radius is enlarged due to atmospheric escape, finding that
≥five of these planetary systems may be detectable on the >4σ
level in this scenario. Finally, we note that the assumed host star
coronal temperature, which affects the shape of an X-ray transit, can
also significantly affect our ability to detect the planet.
Description:
To identify which exoplanet transits may be detectable by AXIS and
NewAthena, we first collected a large sample of known transiting
exoplanets. We drew from the NASA Exoplanet Archive (NEA) list of
confirmed exoplanets with a detected transit as of 2024 May 20, using
the default data entries for each planet.
We chose to examine all 224 stars with distances less than 100pc,
excluding early A-type stars. To avoid missing exceptionally bright
systems that are further away, we also considered stars over 100pc
away if they were younger than 1Gyr. We estimated the X-ray flux of
these stars by assuming that they are in the saturated regime, when
the ratio of X-ray and bolometric luminosity is ∼10-3
(Wright+, 2011ApJ...743...48W 2011ApJ...743...48W, 2018MNRAS.479.2351W 2018MNRAS.479.2351W). We then added to
our sample any stars that had an estimated X-ray flux greater than
10-14erg.cm-2.s-1, of which there were 58. We also added the
WASP-180 system into our sample (1.2±1Gyr old and 254pc away), as it
was listed as an interesting target for future X-ray study by
Foster+ (2022AN....34320007F 2022AN....34320007F). This process yielded a list of
283 stars with 416 transiting planets between them. The stars in the
sample had stellar types ranging from A9 to M7.5.
We first investigated the X-ray emission of each star. We searched for
existing measurements of our sample stars from XMM-Newton, Chandra,
ROSAT, and eROSITA and examined 22 stellar X-ray studies in the
literature that report X-ray observations of at least one star in our
sample. We additionally queried the 4XMM-DR12, XMMSSC, CXOGSGSRC, and
XMMSLEWFUL catalogs. In total, we found X-ray flux measurements for
73 stars in our sample.
For stars with no previous X-ray measurement, we estimated the X-ray
luminosity based on empirical relationships between X-ray emission and
stellar age or rotation period. See Section 2.1.
This process left us with a final sample of 238 stars, 73 of which
have measured X-ray fluxes reported in the literature. Of the 165
stars with estimated fluxes, 67 were based on the W18
(Wright+ 2018MNRAS.479.2351W 2018MNRAS.479.2351W) stellar rotation period relation, 54 on
the J12 (Jackson+ 2012, J/MNRAS/422/2024) stellar age relation using a
measured age, and 44 on the J12 relation using a randomized age.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 142 238 X-ray information and sources table
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/xmm : XMM-Newton Observation Log (XMM-Newton Science Operation Center, 2012-)
IX/11 : ROSAT Source Catalog (Voges+ 1994)
IX/59 : XMM-N Serendipitous Source Catalogue 4XMM-DR9 (Webb+, 2020)
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
IX/65 : XMM-Newton Serendipitous Source Cat. 4XMM-DR11 (Webb+, 2022)
IX/63 : XMM-Newton Serendipitous Source Cat. 4XMM-DR10 (Webb+, 2022)
IX/69 : XMM-Newton Serendipitous Source Cat. 4XMM-DR13 (Webb+, 2023)
IX/68 : XMM-Newton Serendipitous Source Cat. 4XMM-DR12 (Webb+, 2023)
J/A+AS/135/319 : ROSAT data of Nearby Stars (Huensch+ 1999)
J/A+A/397/147 : Activity-rotation relationship in stars (Pizzolato+ 2003)
J/ApJ/743/48 : Stars with rotation periods & X-ray L (Wright+, 2011)
J/MNRAS/422/2024 : X-ray-age relation & exoplanet evaporation (Jackson+, 2012)
J/MNRAS/463/1844 : M dwarfs rotation-activity relation (Stelzer+, 2016)
J/ApJS/224/40 : Catalog of Chandra ACIS point like sources (Wang+, 2016)
J/AJ/154/109 : CKS. III. Planet radii (Fulton+, 2017)
J/AJ/153/136 : Planets & their host stars: Gaia parallaxes (Stassun+, 2017)
J/AJ/156/264 : CKS. VII. Planet radius gap (Fulton+, 2018)
J/ApJ/875/29 : Spectroscopic analysis of CKS sample. I. (Martinez+, 2019)
J/A+A/623/A57 : WASP-121 b Swift UVOT near-UV transit obs (Salz+, 2019)
J/AJ/159/100 : Flux & RVs of the dwarf G9-40: K2 & HPF (Stefansson+, 2020)
J/A+A/650/A66 : DS Tuc A radial velocity curve (Benatti+, 2021)
J/AJ/164/110 : HST/COS far-UV spec AU Microscopii flares (Feinstein+, 2022)
J/A+A/661/A23 : Exoplanet X-ray evaporation rates (Foster+, 2022)
J/A+A/661/A29 : First eROSITA study of nearby M dwarfs (Magaudda+, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Name of planet host star
13- 20 E8.3 pc Dist [6/1080] Distance to system
22- 40 A19 --- r_Dist Distance source (1)
42- 49 E8.3 10-7W Lx [3.8e+25/6.4e+30] 0.2-2.4keV X-ray
luminosity in erg/s
51- 58 E8.3 mW/m2 Fx [5.0e-17/4.3e-11] 0.2-2.4keV X-ray
unabsorbed flux in erg/s/cm2
60- 139 A80 --- r_Lx X-ray luminosity source, ADS bibcode or
description
141- 142 I2 --- Flag ? Estimation flag (2)
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Note (1): Distance source (ADS bibcode) or "1" indicating Gaia DR3
(Cat. I/337, I/356, I/357, I/358, I/359, I/360)
Note (2): Estimation flags as follows:
0 = measured;
1 = estimated from rotation period (Wright+ 2018MNRAS.479.2351W 2018MNRAS.479.2351W);
2 = estimated from age (Jackson+ 2012, J/MNRAS/422/2024);
3 = estimated from a randomized age (Jackson+ 2012, J/MNRAS/422/2024).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 27-May-2025