J/AJ/170/293 HWO: UV & X-ray catalog from archival data (Peacock+, 2025)
HWO target stars and systems: A survey of archival UV and X-Ray data.
Peacock S., Wilson D.J., Richey-Yowell T., Tuchow N.W., France K.,
Caballero J.A., Spinelli R., Corrales L., Zelakiewicz A.S., Redfield S.,
Rockcliffe K., Youngblood A., Froning C.S., Duvvuri G.M., Binder B.A.,
Hinkel N.R., Mamajek E.E.
<Astron. J., 170, 293 (2025)>
=2025AJ....170..293P 2025AJ....170..293P
ADC_Keywords: X-ray sources; Photometry; Spectra, ultraviolet; Exoplanets;
Stars, distances; Space observations; MK spectral classification;
Abundances, [Fe/H]; Combined data; H I data
Keywords: Stellar astronomy ; Ultraviolet astronomy ; X-ray astronomy ;
Stellar atmospheres ; Stellar chromospheres ; Stellar coronae ;
Catalogs ; Astronomical reference materials
Abstract:
We assess archival high-energy data for key stars on the Habitable
Worlds Observatory (HWO) Target Stars and Systems 2025 list, as
stellar radiation is critical to shaping and interpreting planetary
atmospheres. Using a sample of 98 nearby stars (HWO Tier 1 targets),
we compile and evaluate X-ray and ultraviolet (UV) data from archival
eROSITA, Chandra, XMM-Newton, ROentgen SATellite, Extreme-Ultraviolet
Explorer, Swift, Far Ultraviolet Spectroscopic Explorer, International
Ultraviolet Explorer (IUE), Galaxy Evolution Explorer, and Hubble
Space Telescope (HST). We examine spectral and temporal coverage,
assess data quality, and identify major gaps. UV data are moderately
available, with most coverage coming from near-UV spectra from IUE.
Far fewer stars have far-UV spectra, especially from HST. In the X-ray
regime, some stars have high-quality spectra, while others are limited
to shallow detections or broadband photometry. A small fraction of the
sample has both X-ray and UV spectra of sufficient quality to support
full spectral energy distribution modeling. Truly comprehensive
coverage across X-ray, extreme-UV, and both UV bands remains extremely
rare. Most data sets are single-epoch, limiting assessments of
variability and flares-key factors in atmospheric photochemistry and
escape. Moreover, the lack of simultaneous or contemporaneous
observations across bands adds further uncertainty. Our findings
underscore the need for new space-based missions and coordinated
multiwavelength campaigns, ideally with overlapping coverage, to
improve stellar characterization for HWO. As several key observatories
age and face potential decommissioning, there is a narrow window of
opportunity to secure these critical data. Investing in this effort
now will directly support the science goals of HWO and enhance future
studies of planetary habitability.
Description:
### Summary:
We focus on a sample of 98 nearby stars, selected from the most promising
candidates ("Tier 1", 164 stars; Harada+2024, J/ApJS/272/30) in the HWO
Target Stars and Systems 2025 list (TSS25; Tuchow+2025, J/PASP/137/J4402).
We then survey the available high-energy data for these stars across a
broad suite of space-based observatories. These include X-ray
observatories (eROSITA, Chandra, XMM-Newton, ROSAT, and Swift), as
well as UV missions (EUVE, FUSE, IUE, GALEX, and HST).
### Sample:
This analysis focuses on the highest-priority target stars for the
Habitable World Observatory (HWO). The Target Stars and Systems (TSS)
sub-working group constructed the TSS25 list of potential target stars
for HWO's direct imaging survey (Tuchow+2025, J/PASP/137/J4402) from
existing catalogs: the HWO Preliminary Input Catalog (HPIC;
Tuchow+2024, J/AJ/167/139) and the NASA Exoplanet Exploration
Program's Mission Star List for HWO (hereafter referred to as the
"ExEP list"; Mamajek & Stapelfeldt, 2024arXiv240212414M 2024arXiv240212414M). The TSS25
list contains approximately 13,000 stars, broken into three tiers.
This study focuses on a subset of Tier 1 stars, which presently
consists of the 164 stars from the ExEP HWO target list, which can be
found in Harada+2024 (J/ApJS/272/30). For this study, we restricted
our sample to the highest-priority stars (ExEP Tiers A and B)
resulting in a final list of 98 stars.
### Observations:
--- The extended ROentgen Survey with an Imaging Telescope Array
(eROSITA) instrument aboard the Spectrum-Roentgen-Gamma (SRG) mission
provides soft X-ray coverage in the 0.2-2.3keV regime. We found 37 of
our target stars within the first eROSITA public data release (eRASS1;
Merloni+2024, J/A+A/682/A34), which covers the initial six months of
the mission (2019 December-2020 June).
--- The Chandra X-ray Observatory is optimized for high-resolution imaging
and spectroscopy in the soft X-ray regime (0.5-7keV; ∼1-25Å).
Chandra data were compiled from the ChaSeR Chandra archive, and a
total of eight stars were found to have been observed, although three
were not detected. All observations were performed with the Advanced
CCD Imaging Spectrometer (ACIS) instrument. Each detected star has
been analyzed in detail by Binder+2024 (J/ApJS/275/1).
--- The XMM-Newton observatory covers a broad soft X-ray energy range
(0.15-12keV; ∼1-80Å). We queried the XMM-Newton Science Archive and
retrieved a total of 28 stars, including two unresolved binaries.
Of these, five targets were not detected. All observations were
processed and analyzed by Binder+2024 (J/ApJS/275/1).
--- The Roentgen Satellit (ROSAT) conducted the first imaging all-sky
survey in soft X-rays, operating in the 0.1-2.4keV energy range with
the Position Sensitive Proportional Counter. Of the target stars, a
total of 70 have reported count rates in the second ROSAT all-sky
survey (2RXS; Boller+2016, J/A+A/588/A103). Four do not have a 1RXS
counterpart (IX/10A), and an additional three lack reported hardness
ratios. We also flag 11 stars that are likely unresolved binaries.
--- The Extreme Ultra-Violet Explorer (EUVE) operated from 1992-2001
and provided photometric and spectroscopic coverage across several
bands in the EUV (70-760Å). In the EUVE Deep Survey point source
catalog (Bowyer+1996, II/203A, IX/35), we identified 24 targets with a
photometric detection in at least one EUVE band, typically in the
70-190Å range. Only two targets in our sample had spectra that
appeared qualitatively distinct from the sky background.
--- The Neil Gehrels Swift Observatory conducts rapid-response,
short-exposure X-ray observations (0.3-10keV) using the X-Ray
Telescope (XRT) instrument. Its Ultraviolet/Optical Telescope (UVOT)
adds the ability to detect NUV fluxes in a similar bandpass to GALEX
and offered simultaneous UV and X-ray coverage. Using NASA's HEASARC
Swift search portal, we found that a total of 21 Tier 1 stars were
imaged with the XRT instrument, of which four are unresolved binaries.
Seven of the 21 stars were also detected with the UVOT/UM2 filter
(1600-3110Å).
--- The Far Ultraviolet Spectroscopic Explorer (FUSE) observed the FUV
bandpass from 912-1187Å between 1999 and 2007. We used MAST's FUSE
search portal and found only eight targets with observations.
--- The International Ultraviolet Explorer (IUE) provided UV spectra
in both short-wavelength (SWP; 1150-2000Å) and long-wavelength
(LWP/LWR; 1850-3350Å) modes, taken between 1978 and 1996. We
retrieved a list of available IUE data sets for our targets from the
MAST archive, and found that 62 of the 98 stars have at least some IUE
data available, with 33 of these stars having data in at least one
mode classified as usable.
--- The Galaxy Evolution Explorer (GALEX) provided uniform, wide-area
photometric coverage in both the FUV (1350-1750Å) and NUV
(1750-2800Å), with Observations conducted between 2003 and 2012. We
then queried the GALEX MAST catalog and identified 36 of the 98 stars
with viable photometric measurements in at least one band. Of these,
34 stars had FUV data and 13 had NUV data, with 11 stars detected in
both bands. In addition to these detections, 21 stars were observed but
not detected in the NUV, and four were similarly undetected in the FUV.
--- The Hubble Space Telescope (HST) provides low-, medium- and
high-resolution UV spectroscopy across both the FUV (∼1060-1750Å)
and NUV (∼1750-3200Å) regimes through multiple observing modes,
primarily using the Cosmic Origins Spectrograph (COS) and the Space
Telescope Imaging Spectrograph (STIS). To assess HST coverage for our
targets, we cross-matched our sample with both the LOWLIB and the HASP
catalogs. For LOWLIB, we identified 27 stars with available spectra.
For HASP, we found that 25 stars have data in at least one FUV mode,
and 30 have data in at least one NUV mode. Twenty-one targets have
coverage in both regimes.
Earlier in its mission, HST also employed the Goddard High Resolution
Spectrograph (GHRS), which operated from 1990-1997 and provided
high-resolution spectroscopy in the 1150-3200Å range. Thirteen
targets were observed with GHRS, but only 11 have usable observations.
Of these 11, one has FUV-only data, six have NUV-only, and four have
both FUV and NUV.
In total, 52 stars in our sample have usable-quality COS, STIS, and/or
GHRS ultraviolet spectra, with four showing FUV-only coverage, 18 with
NUV-only, and 30 with data in both regimes.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
targets.dat 28 98 List of ExEP Tiers A and B stars (added by CDS)
table2.dat 267 598 *HWO TSS high energy emission data catalog
table3.dat 89 164 Modeled NUV fluxes for TSS25 Tier 1 stars
table4.dat 75 164 *LISM column densities for TSS25 Tier 1 stars
--------------------------------------------------------------------------------
Note on table2.dat: The stellar parameters for "HD 46588 A" were corrected in
VizieR and therefore differ from the online article.
Note on table4.dat: The erroneous entry for HD 46588 A was removed in the
VizieR version; the target already appears correctly later in the table
under its TIC ID, bringing the number of targets to the correct total
of 164, as in Table 3.
--------------------------------------------------------------------------------
See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
II/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011)
II/335 : Revised catalog of GALEX UV sources (GUVcat_AIS GR6+7) (Bianchi+ 2017)
II/203A : Second Extreme Ultra-Violet Explorer Catalog (2EUVE, 1997)
III/135A : Henry Draper Catalogue and Extension (Cannon+ 1918-1924; ADC 1989)
IV/39 : TESS Input Catalog version 8.2 (TIC v8.2) (Paegert+, 2021)
VI/110 : Final Merged Log of IUE Observations (NASA-ESA, 2000)
IX/10A : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
IX/35 : Second EUVE Catalogues (Bowyer+, 1996-99)
IX/69 : XMM-Newton Serendipitous Source Catalogue 4XMM-DR13 (Webb+, 2023)
IX/70 : Chandra Source Catalog Release 2 (CSC 2.1) (Evans+, 2024)
J/ApJ/657/1046 : Synthetic Mid-UV spectr. indices of stars (Chavez+, 2007)
J/ApJS/187/149 : StarCAT: STIS UV echelle spectra of stars (Ayres, 2010)
J/ApJ/761/166 : Terrestrial exoplanet atmospheres. I. (Hu+, 2012)
J/A+A/588/A103 : Second ROSAT all-sky survey (2RXS) source cat. (Boller+, 2016)
J/MNRAS/489/5046 : GALEX absolute calib. based on white dwarfs (Wall+, 2019)
J/A+A/664/A105 : Stellar content of the ROSAT all-sky survey (Freund+, 2022)
J/AJ/163/67 : 5-55000Å spectrum of TOI 560 (Zhang+, 2022)
J/ApJS/275/1 : X-ray obs. of potential host star's HZ (Binder+, 2024)
J/ApJS/272/30 : Habitable Worlds Observatory (HWO): 164 targets (Harada+, 2024)
J/A+A/682/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)
J/AJ/167/139 : HPIC catalog & potential contaminants from Gaia (Tuchow+, 2024)
J/A+A/693/A285 : Spectr. Energy Distribution of 100 stars (Sanz-Forcada+, 2025)
J/PASP/137/J4402 : HWO Target Stars & Systems 2025 list (TSS25) (Tuchow+, 2025)
Byte-by-byte Description of file: targets.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- HD Henry Draper Catalog (III/135A) ID
13- 26 A14 --- TIC TESS Input Catalog (IV/39) ID
28 A1 --- ExEP ExEP tier classification (A or B) (1)
--------------------------------------------------------------------------------
Note (1): ExEP tier classification (Mamajek & Stapelfeldt, 2024arXiv240212414M 2024arXiv240212414M)
as follows:
A = 48 occurrences
B = 50 occurrences
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- HD Henry Draper Catalog (III/135A) ID
13- 26 A14 --- TIC TESS Input Catalog (IV/39) ID
28- 40 F13.9 deg RAdeg Right ascension at epoch J2000 (ICRS)
42- 54 F13.9 deg DEdeg Declination at epoch J2000 (ICRS)
56- 60 F5.3 mag Vmag [0.01/7.52] Apparent Johnson V magnitude
62- 73 F12.9 pc Dist [1.34/21.78] Distance
75- 89 A15 --- SpType Spectral type
91- 94 I4 K Teff [3469/6782] Effective temperature
96 A1 --- ExEP ExEP tier classification (A or B)
98- 107 A10 --- Obs Observatory used for observation (1)
109- 119 A11 --- Inst Instrument used for observation (2)
121- 138 A18 --- Mode Observing mode
140- 151 A12 --- Type Observation type (3)
153- 157 A5 --- Band General wavelength band (4)
159- 169 A11 --- Wave Wavelength coverage of observation in
Angstroms
171- 197 A27 --- Quality Description of data quality
199 I1 --- Flag [0/2] Quality flag (5)
201- 267 A67 --- URL URL for where to access the data
--------------------------------------------------------------------------------
Note (1): Observatory as follows:
Chandra = The Chandra X-ray Observatory, optimized for high-resolution
imaging and spectroscopy in the soft X-ray regime
(8 occurrences)
EUVE = The Extreme Ultra-Violet Explorer (EUVE), providing photometric
and spectroscopic coverage across several bands in the EUV
(28 occurrences)
FUSE = The Far Ultraviolet Spectroscopic Explorer (FUSE), observed
the FUV bandpass (8 occurrences)
GALEX = The Galaxy Evolution Explorer (GALEX), provided uniform
wide-area photometric coverage in both the FUV and NUV
(47 occurrences)
HST = The Hubble Space Telescope (HST), providing low-, medium- and
high-resolution UV spectroscopy across both the FUV and NUV
(150 occurrences)
IUE = The International Ultraviolet Explorer (IUE), provided UV
spectra in both short-wavelength and long-wavelength modes
(194 occurrences)
ROSAT = The Roentgen Satellit (ROSAT), conducted the first imaging
all-sky survey in soft X-rays (70 occurrences)
Swift = The Neil Gehrels Swift Observatory, conducting rapid-response,
short-exposure X-ray observations as well as simultaneous UV
and X-ray coverage (28 occurrences)
XMM-Newton = The XMM-Newton observatory, covering a broad soft X-ray energy
range (28 occurrences)
eROSITA = The extended ROentgen Survey with an Imaging Telescope Array
(eROSITA) instrument aboard the Spectrum-Roentgen-Gamma (SRG)
mission, providing soft X-ray coverage (37 occurrences)
Note (2): Instrument as follows:
ACIS = Advanced CCD Imaging Spectrometer (ACIS) on Chandra
(8 occurrences)
COS = Cosmic Origins Spectrograph (COS) on HST (18 occurrences)
GHRS = Goddard High Resolution Spectrograph (GHRS) on HST
(33 occurrences)
STIS = Space Telescope Imaging Spectrograph (STIS) on HST
(99 occurrences)
FUV Channel = Far-UV channel on GALEX (34 occurrences)
NUV Channel = Near-UV channel on GALEX (13 occurrences)
DS = Deep Survey (DS) imager on EUVE (24 occurrences)
Spec = Spectrometer on EUVE (4 occurrences)
UVOT = Ultraviolet/Optical Telescope (UVOT) on Swift (7 occurrences)
XRT = X-Ray Telescope (XRT) on Swift (21 occurrences)
pspc = Position Sensitive Proportional Counter (pspc) on ROSAT
(70 occurrences)
Note (3): Observation types as follows:
Photometry = 206 occurrences
Spectroscopy = 392 occurrences
Note (4): Band as follows:
EUV = Extreme ultraviolet (28 occurrences)
FUV = Far ultraviolet (184 occurrences)
NUV = Near ultraviolet (222 occurrences)
X-ray = X-ray (164 occurrences)
Note (5): Quality flag as follows:
0 = Poor quality data (112 occurrences)
1 = Usable data (377 occurrences)
2 = Data with known issues (109 occurrences)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- Name Star name
16- 19 I4 K Teff [3469/6962] Effective temperature (1)
21- 24 F4.2 [-] logg [3.61/4.78] Log of surface gravity (1)
26- 30 F5.2 [-] [Fe/H] [-1.33/0.38] Metallicity (1)
32- 36 F5.2 pc Dist [1.35/23.29] Distance (1)
38- 40 F3.1 Rsun Rad [0.4/2.4] Radius (1)
42- 47 F6.2 [mW/cm2] [FNUV] [-15.27/-9.96] Log of GALEX NUV flux;
erg/s/cm2 (2)
49- 54 F6.2 [mW/cm2] [F2500-4000] [-12.8/-8.88] Log of flux in 2500-4000
Angstrom band; erg/s/cm2 (2)
56- 61 F6.2 [mW/cm2] [F2000-2500] [-16.25/-10.17] Log of flux in
2000-2500 Angstrom band; erg/s/cm2 (2)
63- 68 F6.2 [mW/cm2] [F2500-3000] [-14.26/-9.38] Log of flux in
2500-3000 Angstrom band; erg/s/cm2 (2)
70- 75 F6.2 [mW/cm2] [F3000-3500] [-12.9/-8.79] Log of flux in 3000-3500
Angstrom band; erg/s/cm2 (2)
77- 82 F6.2 [mW/cm2] [F3500-4000] [-12.45/-8.7] Log of flux in 3500-4000
Angstrom band; erg/s/cm2 (2)
84- 89 F6.2 [mW/cm2] [F4000-4500] [-11.8/-8.43] Log of flux in 4000-4500
Angstrom band; erg/s/cm2 (2)
--------------------------------------------------------------------------------
Note (1): Stellar parameters are adopted directly from the HPIC catalog
(J/AJ/167/139).
Note (2): Estimated NUV fluxes for TSS25 Tier 1 stars computed using BT-Settl
PHOENIX stellar atmosphere models. All fluxes are scaled to Earth.
The GALEX NUV fluxes are calculated by convolving the model spectra
with the GALEX NUV transmission curve (shown in Figure 8), while
fluxes in the other wavelength bands are computed from flat (boxcar)
integrations.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- Name Star name
16 A1 --- f_Name Flag on Name (1)
18- 30 F13.9 deg RAdeg Right ascension (J2000)
32- 44 F13.9 deg DEdeg Declination (J2000)
46- 50 F5.2 pc Dist [1.35/23.29] Distance
52- 56 F5.2 [cm-2] logNHI-e [17.61/18.8] Estimated column density (2)
58- 61 F4.2 [cm-2] e_logNHI-e [0.22/0.36] Uncertainty in logNHI-e
63- 67 F5.2 [cm-2] logNHI-m [17.61/18.8]? Measured column density (3)
69- 72 A4 --- Source Source of column densities (5)
74- 75 I2 --- Ref [1/16]? Reference (4)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
* = high-resolution spectra available that could yield measured values, but
these spectra have not yet been analyzed.
Note (2): Estimated values from the LISM_NHI tool from
Youngblood+2025 (J/AJ/170/342).
Note (3): Measured values for Tier A and B stars are derived directly from HI
observations, or scaled from MgII or FeII observations, as specified
by Source column.
Note (4): References as follows:
1 = Wood+2005 (2005ApJS..159..118W 2005ApJS..159..118W)
2 = Malamut+2014 (2014ApJ...787...75M 2014ApJ...787...75M)
3 = Redfield+2002 (2002ApJ...581..626R 2002ApJ...581..626R)
4 = Linsky+1996 (1996ApJ...463..254L 1996ApJ...463..254L)
5 = Redfield+2004 (2004ApJ...602..776R 2004ApJ...602..776R)
6 = Nisak+2025 (2025ApJ...983....5N 2025ApJ...983....5N)
7 = Wood+2000b (2000ApJ...537..304W 2000ApJ...537..304W)
8 = Wood+2000a (2000ApJ...542..411W 2000ApJ...542..411W)
9 = Zachary+2018 (2018ApJ...859...42Z 2018ApJ...859...42Z)
10 = Edelman+2019 (2019ApJ...880..117E 2019ApJ...880..117E)
11 = Wood+1998 (1998ApJ...492..788W 1998ApJ...492..788W)
12 = Youngblood+2022 (2022ApJ...926..129Y 2022ApJ...926..129Y)
13 = Wood+1996 (1996ApJ...470.1157W 1996ApJ...470.1157W)
14 = Wood+2021 (2021ApJ...915...37W 2021ApJ...915...37W)
15 = Vannier+2025 (2025ApJ...981..102V 2025ApJ...981..102V)
16 = Wood+2014 (2014ApJ...781L..33W 2014ApJ...781L..33W)
Note (5): Column density source as follows:
HI = Derived directly from HI observations (26 occurrences)
FeII = Scaled from FeII observations (2 occurrences)
MgII = Scaled from MgII observations (6 occurrences)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 18-Aug-2026