J/MNRAS/541/1866 NGC 7419 membership and variability (Chakraborty+, 2025)
Exploring membership and variability in NGC 7419:
an open cluster rich in supergiants and Be type stars.
Chakraborty A., Jose J., Carciofi A.C.
<Mon. Not. R. Astron. Soc. 541, 1866 (2025)>
=2025MNRAS.541.1866C 2025MNRAS.541.1866C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, emission ; Stars, Be ; Stars, variable
Keywords: methods: data analysis - methods: statistical -
stars: emission-line, Be - stars: variables: general
Abstract:
NGC 7419 is a young open cluster notable for hosting five red
supergiants and a high abundance of Classical Be (CBe) stars. CBe
stars are main-sequence non-supergiant B-type stars that exhibit or
have exhibited Balmer-line emissions in their spectra. We perform a
membership analysis using Gaia DR3 data and machine learning
techniques like Gaussian mixture models and Random Forest and
determine the cluster's mean distance to be 3.6+1.0-0.6kpc. We
identify 499 Gaia-based members with a mass above ∼1.2M☉, and
estimate the cluster's age to be 21.1+1.6-0.6Myr. Using our
revised Halpha excess-based analysis, we find 42 CBe stars containing
many known CBe stars, bringing the total number of CBe stars in
NGC 7419 to 49 and the fraction of CBe to (B + CBe) members to 12.7
per cent. We investigate the variability of the candidate members from
Zwicky Transient Facility and NEOWISE data using standard deviation,
median absolute deviation, and Stetson index (J), and their
periodicity using the Generalized Lomb-Scargle periodogram
variability. We find that 66 per cent of CBe stars are variable: 23
per cent show periodic signals, typical of pulsation/rotation, 41 per
cent display variability characteristic of disc dynamics or binarity,
and 14 per cent exhibit long-term changes, consistent with disc
dissipation/formation. We also find that all pulsating CBe stars are
early-type, while 50 per cent of stars with long-term variations are
early-type, and the other 50 per cent are mid-type. Our results agree
with previous findings in the literature and confirm that CBe stars
display variability through multiple mechanisms across different
time-scales.
Description:
We studied the open cluster NGC 7419, which stands out due to its high
number of CBe stars and five red supergiants. Even though
spectroscopic analysis of cluster members has been done in previous
literature (Subramaniam et al., 2006MNRAS.370..743S 2006MNRAS.370..743S; Marco &
Negueruela, 2013A&A...552A..92M 2013A&A...552A..92M, Cat. J/MNRAS/552/A92), no study has
examined the variability of these members.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 87 499 NGC 7419 members
table2.dat 72 288 Variability and periodicity of NGC 7419 members
in ZTF r band data
table3.dat 69 149 Variability and periodicity of NGC 7419 members
in NEOWISE data
table4.dat 104 373 NGC 7419 B-type members
--------------------------------------------------------------------------------
See also:
J/other/BASI/39.517 : Spectroscopy of classical Be stars (Mathew+, 2011)
J/ApJS/208/9 : PMS stars intrinsic colors & temperatures (Pecaut+, 2013)
J/A+A/552/A92 : uvby photometry in NGC 7419 (Marco+, 2013)
J/ApJS/93/187 : UBV Photometry in NGC 7419 (Beauchamp+ 1994)
J/MNRAS/391/1279 : Multiwavelength study of NGC 7419 (Joshi+, 2008)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- StarID Unique identifier for each NGC 7419 member
5- 23 I19 --- GaiaDR3 Unique Gaia DR3 source identifier
25- 33 F9.5 deg RAdeg Right Ascension of the star (ICRS) at Ep=2016
35- 42 F8.5 deg DEdeg Declination of the star (ICRS) at Ep=2016
44- 49 F6.4 mas Plx Parallax
51- 56 F6.3 mas/yr pmRA Proper motion in Right Ascension
58- 63 F6.3 mas/yr pmDE Proper motion in Declination
65- 69 F5.2 mag Gmag Gaia G-band apparent magnitude
71- 75 F5.2 mag BPmag Gaia blue photometric band apparent magnitude
77- 81 F5.2 mag RPmag Gaia red photometric band apparent magnitude
83- 87 F5.3 --- pmemb ? Probability that the star is a member
of NGC 7419 (1)
--------------------------------------------------------------------------------
Note (1): The 2 stars (Red SGs) that have null membership probability were not
classified as members by our algorithm as they had probability less than 0.9,
but were added later as they are well known members of NGC 7419.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- StarID Unique identifier for each NGC 7419 member
5- 20 I16 --- OId ZTF object identifier
22- 30 F9.5 deg RAdeg Right Ascension of the star (J2000)
32- 39 F8.5 deg DEdeg Declination of the star (J2000)
41- 45 F5.2 mag rmag Apparent r-band magnitude of the star
47- 53 F7.2 --- StetsonIndex Stetson variability index, a measure of
variability
55 I1 --- Var [0/1]? Indicates if the star is variable
or not
57- 64 F8.4 d Per1 ? Period 1 of variability in r-band
66- 72 F7.4 d Per2 ? Period 2 of variability in r-band
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- StarID Unique identifier for each NGC 7419 member
5- 13 F9.5 deg RAdeg Right Ascension of the star (J2000)
15- 22 F8.5 deg DEdeg Declination of the star (J2000)
24- 28 F5.2 mag W1mag Apparent magnitude of the star in
the W1 band
30- 34 F5.2 mag W2mag Apparent magnitude of the star in
the W2 band
36- 42 F7.2 --- StetsonIndex Stetson variability index, a measure of
variability
44 I1 --- Var [0/1]? Indicates if the star is variable
or not
46- 53 F8.4 d PerW1 ? Period of variability in the W1 band
55- 62 F8.4 d PerW2-1 ? Period 1 of variability in the W2 band
64- 69 F6.4 d PerW2-2 ? Period 2 of variability in the W2 band
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- StarID ? Unique identifier for each NGC 7419
member (1)
5- 13 F9.5 deg RAdeg Right Ascension of the star (ICRS) at Ep=2016
15- 22 F8.5 deg DEdeg Declination of the star (ICRS) at Ep=2016
24- 38 A15 --- SpType Spectral type of the source (2)
40- 43 F4.2 Rsun Radius ? Stellar radius estimated from modified
table of Pecaut and Mamajek
(2013ApJS..208....9P 2013ApJS..208....9P, Cat. J/ApJS/208/9)
45- 49 F5.2 Msun Mass ? Stellar mass estimated from modified table
of Pecaut and Mamajek
(2013ApJS..208....9P 2013ApJS..208....9P, Cat. J/ApJS/208/9)
51- 56 F6.2 km/s Vbreakup ? Breakup or critical velocity estimated
using our estimated mass and radius
58 I1 --- VarZTF [0/1]? Indicates whether the star is variable
or not
60 I1 --- VarNEOWISE [0/1]? Indicates whether the star is variable
or not
62- 69 F8.4 d PerZTF1 ? Period 1 of variability in ZTF r-band
71- 77 F7.4 d PerZTF2 ? Period 2 of variability in ZTF r-band
79- 86 F8.4 d PerW1 ? Period of variability in NEOWISE W1 band
88- 95 F8.4 d PerW2-1 ? Period 1 of variability in NEOWISE W2 band
97-102 F6.4 d PerW2-2 ? Period 2 of variability in NEOWISE W2 band
104 I1 --- CBe [0/1]? Indicates whether the star is a CBe
star or not
--------------------------------------------------------------------------------
Note (1): The last two stars in the table are CBe stars, which have no
masses/radii/breakup velocities reported, are the CBe members from previous
literature (Mathew & Subramaniam, 2011BASI...39..517M 2011BASI...39..517M, Cat J/other/BASI/39.517)
that do not have Gaia data available.
Note (2): Superscripts (a) and (b) indicate spectral types from previous
literature and our estimates respectively.
--------------------------------------------------------------------------------
Acknowledgements:
From Arghya Chakraborty, chakrabortyarghya233(at)gmail.com
We acknowledge the partial support from the grant RJF/2020/000071 as a
part of the Ramanujan Fellowship (PI: Eswaraiah Chakali) awarded by
the Science and Engineering Research Board (SERB). JJ acknowledges the
financial support from the DST-SERB grant SPG/2021/003850. ACC
acknowledges support from CNPq (grant 314545/2023-9) and FAPESP
(grants 2018/04055-8 and 2019/13354-1).
(End) Patricia Vannier [CDS] 29-Dec-2025