J/A+A/702/A218 NGC 2516 eROSITA X-ray observations (Fritzewski+, 2025)
A star-by-star correspondence between X-Ray activity and rotation in the young
open cluster NGC 2516 with eROSITA.
Fritzewski D.J., Barnes S.A., Ok S., Lamer G., Schwope A.
<Astron. Astrophys. 702, A218 (2025)>
=2025A&A...702A.218F 2025A&A...702A.218F (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, late-type ; X-ray sources ; Spectroscopy
Keywords: stars: activity - stars: coronae - stars: late-type -
stars: rotation -
open clusters and associations: individual: NGC2516 - X-rays: stars
Abstract:
The coronal soft X-ray emission of cool stars, especially in
combination with their measured rotation periods, provides insight
into their levels of magnetic activity and related transitions.
We study the X-ray properties of low-mass (FGKM-type) members of the
open cluster NGC 2516 to explicate their detailed dependencies on mass
and rotation.
We analyse the pointed SRG/eROSITA satellite observations of NGC 2516
obtained during the calibration and performance verification phase of
the mission. We find 1561 X-ray sources within the field of view. Of
these we relate 1007 to optical stellar counterparts, including 655
members of NGC 2516, 433 of which have measured rotation periods. We
combine these detections with auxiliary optical data to enable
interpretation. Furthermore, we extract X-ray spectra for all sources
and fit two-component APEC models to them. To aid analysis, we group
stars with similar mass and rotational properties, allowing us to
investigate the influence of rotation on various X-ray properties.
The colour-activity diagram of NGC 2516 shows a general increase of
the fractional X-ray luminosity with spectral type change from F
through G and K to M-type. However, the behaviour of K-type stars,
representing those best sampling the fast- to slow rotational
transition, is more complex, with both increased and decreased X-ray
emission relative to G-type stars for fast and slow rotators
respectively. The rotation-activity diagram is analogous, with an
identifiable desaturated group of X-ray emitters that corresponds to
stars in the rotational gap between the fast and slow rotator
sequences. We prefer describing the normalized X-ray emission for all
cluster stars as declining logarithmically with Rossby number over
those using broken power laws. Coronal temperatures appear to be
largely independent of mass or rotation. The coronal abundances are
significantly sub-solar for most stars, as in prior work, but
near-solar for both the least-active stars in our sample and a number
of the very active stars.
The wealth of X-ray detections and rotation periods for stars in NGC
2516 enables a detailed view of the connection between rotation and
X-ray activity in a homogeneous and coeval cluster sample of young
stars.
Description:
We present the pointed eROSITA observations of the open cluster
NGC 2516.
Table 2 contains the positions, counts, and X-ray fluxes for all
sources within the field of view.
Table 3 provides the APEC model fits to all X-ray spectra under the
assumption that these sources are coronal emitters and NGC 2516
cluster members.
Table 4 gives the cross-match between the X-ray sources from Table 1
and Gaia DR3. Further, it holds membership information and rotational
properties from the literature as well as the derived solar-scaled
Rossby numbers.
Table B1 includes additional power-law fits to the X-ray spectra of
sources without stellar counterparts.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 69 1561 All eROSITA detections in the field of view
table3.dat 96 640 *APEC fits of stellar sources
table4.dat 123 995 Optical counterparts as matched with Gaia DR3
tableb1.dat 74 608 Power-law spectra of non-stellar sources
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Note on table3.dat: Column density fixed to the cluster value of
NH=1022cm-2.
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/A+A/450/993 : XMM survey of NGC 2516 (Pillitteri+, 2006)
J/ApJ/588/1009 : Chandra X-ray observations of NGC 2516 (Damiani+, 2003)
J/A+A/641/A51 : NGC 2516 membership list (Fritzewski+, 2020)
J/AJ/162/197 : Photometry, rotation and Li in open cluster NCG 2516
(Bouma+, 2021)
https://erosita.mpe.mpg.de/edr/eROSITAObservations : eROSITA-DE,
Early Data Release site
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- SRCID [1/1634] eROSITA source ID
6- 14 F9.5 deg RAdeg Right ascension (J2000.0)
16- 24 F9.5 deg DEdeg Declination (J2000.0)
26- 33 F8.5 deg ePos ? Positional uncertainty
35- 42 E8.2 s-1 Crate Count rate
44- 51 E8.2 s-1 e_Crate ? Uncertainty on count rate
53- 60 F8.6 10-18W/m2 Flux X-ray flux calculated with ECF for NGC 2516
62- 69 F8.6 10-18W/m2 e_Flux ? Uncertainty on X-ray flux
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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- 4 I4 --- SRCID [2/1629] eROSITA source ID, as in table2
6- 14 F9.5 deg RAdeg Right ascension (J2000.0)
16- 24 F9.5 deg DEdeg Declination (J2000.0)
26- 32 F7.5 deg ePos ? Positional uncertainty
34- 37 F4.2 keV APEC1kT ? Temperature of first APEC component
39- 42 F4.2 keV bAPEC1kT ? Lower bound of first APEC component
44- 47 F4.2 keV BAPEC1kT ? Upper bound of first APEC component
49- 52 F4.2 keV APEC2kT ? Temperature of second APEC component
54- 57 F4.2 keV bAPEC2kT ? Lower bound of second APEC component
59- 63 F5.2 keV BAPEC2kT ? Upper bound of second APEC component
65- 68 F4.2 keV meankT ? Weighted mean temperature of both APEC
components
70- 74 F5.2 keV e_meankT Uncertainty on mean temperature
76- 80 F5.3 --- Abund Abundance of APEC fit
82- 86 F5.3 --- e_Abund Uncertainty on abundance
88- 96 E9.3 --- Prob Null hypothesis probability
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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- 4 I4 --- SRCID [1/1631]? eROSITA source ID, as in table2 (1)
6- 14 F9.5 deg RAdeg ? Right ascension (J2000.0) from eROSITA (1)
16- 24 F9.5 deg DEdeg ? Declination (J2000.0) from eROSIAT (1)
26- 33 A8 --- --- [Gaia DR3]
35- 53 I19 --- GaiaDR3 Gaia DR3 source_id
55- 63 F9.5 deg RAGdeg Right ascension from Gaia DR3 (ICRS)
at Ep=2016.0 (Cat. I/355)
65- 73 F9.5 deg DEGdeg Declination from Gaia DR3 (ICRS)
at Ep=2016.0 (Cat. I/355)
75- 79 I5 K Teff ? Effective temperature derived from
photometry
81- 86 F6.3 mag Gmag G magnitude from Gaia DR3 (Cat. I/355)
88- 93 F6.3 mag (G-RP)0 (G-RP)_0 colour from Gaia DR3 (Cat. I/355)
95- 99 F5.2 [-] logLX/Lbol Fractional X-ray luminosity
101-104 F4.2 [-] e_logLX/Lbol ? Uncertainty on fractional X-ray luminosity
106 I1 --- Member [0/1] Indicates membership status
108-112 F5.2 d Per ? Rotation period from the literature
114-119 F6.4 Sun Ro ? Solar-scaled Rossby number
121-123 F3.1 --- Multiple [1]? Indicates whether two sources are
within 7 arcsec
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Note (1): Stars with missing values in the first three columns are not observed
by eROSITA but Chandra or XMM-Newton.
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- SRCID [4/1634] eROSITA source ID
6- 14 F9.5 deg RAdeg ? Right ascension (J2000.0)
16- 24 F9.5 deg DEdeg ? Declination (J2000.0)
26- 32 F7.3 10+22cm-2 NH Hydrogen column density
34- 39 F6.3 --- PhoIndex Power-law index of spectral fit
41- 46 F6.3 --- b_PhoIndex ?=0 Lower bound of power-law index
48- 53 F6.3 --- B_PhoIndex ?=0 Upper bound of power-law index
55- 63 E9.3 --- PhoIndexnorm Normalization of power-law index
65- 74 E10.3 --- Prob Null hypothesis probability
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Acknowledgements:
Dario Fritzewski, dario.fritzewski(at)kuleuven.be
References:
https://erosita.mpe.mpg.de/edr/eROSITAObservations/CalPvObs/NGC_2516.tar.gz
(End) Patricia Vannier [CDS] 26-Aug-2025