J/A+A/710/A164 NGC 1647 cluster as seen by LAMOST (Frasca+, 2026)
NGC 1647. A young open cluster with a broad main sequence observed with LAMOST.
Frasca A., Qin M., Alonso-Santiago J., Catanzaro G., Fu J.N., Zhang J.Y.,
Bragaglia A.
<Astron. Astrophys. 710, A164 (2026)>
=2026A&A...710A.164F 2026A&A...710A.164F (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Abundances ; Effective temperatures ; Optical ;
Radial velocities ; Rotational velocities; Balmer lines
Keywords: stars: abundances - stars: activity - binaries: spectroscopic -
stars: fundamental parameters -
open clusters and associations: individual: NGC 1647
Abstract:
In this work we present the results of our analysis of
medium-resolution LAMOST spectra of candidate members of the cluster
NGC 1647 with the aim of determining the stellar parameters, activity
level, lithium abundance, and to study the cluster properties.
We used the code ROTFIT to determine the atmospheric parameters (Teff,
logg, and [Fe/H]), radial velocity (Vr), and projected rotation
velocity (vsini). Moreover, for solar-type and cooler stars
(Teff<6500K), we calculated the H-alpha and LiI-6708 net equivalent
width by means of the subtraction of inactive photospheric templates.
We determined the rotation periods for 160 stars by analyzing the
available TESS photometry.
We derived Vr, vsini, and atmospheric parameters for 341 spectra of
155 stars, plus three additional bright targets with archival UVES
spectra. Moreover, we found four double-lined spectroscopic systems
for which we provide the radial velocities of the two components. The
Vr distribution of the cluster members peaks at -5.3km/s with a
dispersion of 1.6km/s, while the average metallicity is
[Fe/H]=-0.08±0.08dex, in line with previous determinations, which
were based on only a handful stars. From the fitting of the spectral
energy distribution of 160 likely members we infer the existence of a
differential reddening across the cluster field with an average value
of Av=1.1mag. The Av values show a distinct correlation with the
color offset from the lower boundary of the main sequence, as observed
in the Gaia color-magnitude diagram; conversely, this offset appears
to be uncorrelated with vsini. These two findings confirm that
differential reddening is the primary driver behind the observed
extended Main-Sequence Turn-Off (eMSTO) in this cluster. The age of
NGC 1647, obtained from the lithium abundance, is 203±27Myr, which
is compatible with the values inferred from a gyrochronological
approach and the isochrone fitting.
Description:
Spectral type, average atmospheric parameters (Teff, logg, and
[Fe/H]), radial velocity (RV) and projected rotational velocity
(vsini) are quoted in Table 1 for 158 stars.
Table 2 reports the H-alpha equivalent width, flux at the stellar
surface and luminosity ratio R'Ha for 85 targets.
Table 3 reports the LiI-6708 equivalent width and lithium abundance
for 87 targets.
Table B.2 lists the radius (R), luminosity (L), and extinction (Av)
that were based on the atmospheric parameters and a fit of spectral
energy distributions (SEDs).
Table B.3 reports the rotation period derived in the present work by
analyzing TESS photometry.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 158 158 Stellar parameters
table2.dat 124 85 Activity indicators
table3.dat 130 87 Lithium equivalent width and abundance
tableb2.dat 102 160 Radius, luminostity, and extinction from the SEDs
tableb3.dat 47 160 Rotation periods from TESS photometry
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See also:
J/A+A/618/A93 : Gaia DR2 open clusters in the Milky Way (Cantat-Gaudin+, 2018)
J/A+A/686/A42 : Improving the open cluster census. III. (Hunt+, 2024)
J/A+A/594/A39 : LAMOST-Kepler parameters and activity indicators
(Frasca+, 2016)
J/A+A/664/A78 : Kepler targets class based on LAMOST spectra (Frasca+, 2022)
J/A+A/698/A7 : Pleiades LAMOST mid-resolution observations (Frasca+, 2025)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Star Star name (1)
22- 29 F8.5 deg RAdeg Right ascension (J2000)
32- 39 F8.5 deg DEdeg Declination (J2000)
42- 60 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
64- 68 I5 K Teff Effective temperature
70- 73 I4 K e_Teff Effective temperature error
77- 80 F4.2 [cm/s2] logg Logarithm of surface gravity
84- 87 F4.2 [cm/s2] e_logg Error on logarithm of surface gravity
90- 94 F5.2 [Sun] [Fe/H] Iron abundance relative to the Sun
97-101 F5.2 [Sun] e_[Fe/H] ?=-1.0 Error on iron abund relative
to the Sun
104 A1 --- l_vsini Limit flag on vsini
107-111 F5.1 km/s vsini Projected rotational velocity
115-118 F4.1 km/s e_vsini ?=-9.9 Projected rotational velocity error
122-128 A7 --- SpType Spectral type in MK or HD
134-136 A3 --- Sample Sample (2)
139-144 F6.2 km/s HRV Average Heliocentric Radial Velocity
146-150 F5.2 km/s e_HRV Heliocentric Radial Velocity error
154-158 A5 --- Remarks Remarks (3)
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Note (1): Star name as follows:
HD number or LAMOST designation
Note (2): Subsample as follows:
C = Cantat Gaudin et al. (2018A&A...618A..93C 2018A&A...618A..93C, Cat. J/A+A/618/A93)
H = Hunt & Reffert (2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42)
Q = Qin et al. (2026ApJ..1002...81Q 2026ApJ..1002...81Q)
Note (3): Remarks as follows:
RVvar = Significantly variable RV (P(chi2)<0.05)
UVES = UVES archival spectra
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Star LAMOST designation (JHHMMSS.ss+DDMMSS.s)
23- 41 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
44- 48 I5 K Teff Effective temperature
51- 54 I4 K e_Teff Effective temperature error
59- 62 F4.2 [cm/s2] logg Logarithm of surface gravity
65- 68 F4.2 [cm/s2] e_logg Error on logarithm of surface gravity
72 A1 --- l_EWHa Limit flag on Hα equivalent width
74- 78 F5.2 0.1nm EWHa Hα equivalent width
80- 84 F5.2 0.1nm e_EWHa Hα equivalent width error
86- 94 E9.4 mW/m2 FHa Hα flux (in erg/cm2/s)
96-104 E9.4 mW/m2 e_FHa Hα flux error (in erg/cm2/s)
107-111 F5.2 --- logRHa logarithm of Luminosity ratio
Hα/Bolometric log(LHα/Lbol)
114-117 F4.2 --- e_logRHa Error of log(LHα/Lbol)
122-124 A3 --- Sample Sample (1)
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Note (1): Subsample as follows:
C = Cantat Gaudin et al. (2018A&A...618A..93C 2018A&A...618A..93C, Cat. J/A+A/618/A93)
H = Hunt & Reffert (2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42)
Q = Qin et al. (2026ApJ..1002...81Q 2026ApJ..1002...81Q)
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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- 19 A19 --- Star LAMOST designation (JHHMMSS.ss+DDMMSS.s)
23- 41 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
45- 53 F9.6 deg RAdeg Right Ascention (J2000)
57- 65 F9.6 deg DEdeg Declination (J2000)
69- 73 I5 K Teff Effective temperature
76- 79 I4 K e_Teff Effective temperature error
84- 87 F4.2 [cm/s2] logg Logarithm of surface gravity
92- 95 F4.2 [cm/s2] e_logg Error on logarithm of surface gravity
100-103 I4 0.1pm EW(Li) Lithium equivalent width
107-109 I3 0.1pm e_EW(Li) rms uncertainty on EW(Li)
112-116 F5.2 [-] A(Li) Lithium abundance
119-123 F5.2 [-] e_A(Li) Error on A(Li)
128-130 A3 --- Sample Sample (1)
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Note (1): Subsample as follows:
C = Cantat Gaudin et al. (2018A&A...618A..93C 2018A&A...618A..93C, Cat. J/A+A/618/A93)
H = Hunt & Reffert (2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42)
Q = Qin et al. (2026ApJ..1002...81Q 2026ApJ..1002...81Q)
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Star Star name (1)
24- 42 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
46- 50 I5 K Teff Effective temperature
52- 55 I4 K e_Teff Effective temperature error
58- 63 F6.3 [Rsun] Rad Radius
67- 71 F5.3 [Rsun] e_Rad Uncertainty on Rad
74- 81 F8.3 [Lsun] Lum Luminosity
84- 89 F6.3 [Lsun] e_Lum Uncertainty on Lum
93- 96 F4.2 [mag] Av V band extinction
99-102 F4.2 [mag] e_Av Uncertainty on Av
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Note (1): Star name as follows:
HD number or LAMOST designation
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Byte-by-byte Description of file: tableb3.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
23- 31 I9 --- TIC TESS Input Catalog identifier
34- 39 F6.3 d Prot Rotation period
43- 47 F5.3 d e_Prot Uncertainty on Prot
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Acknowledgements:
Antonio Frasca, antonio.frasca(at)inaf.it
License: CC-BY-4.0
(End) Antonio Frasca [INAF-OACt, Italy], Patricia Vannier [CDS] 17-Apr-2026