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. =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: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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) -------------------------------------------------------------------------------- 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, Cat. J/A+A/618/A93) H = Hunt & Reffert (2024A&A...686A..42H, Cat. J/A+A/686/A42) Q = Qin et al. (2026ApJ..1002...81Q) Note (3): Remarks as follows: RVvar = Significantly variable RV (P(chi2)<0.05) UVES = UVES archival spectra -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 H{alpha} equivalent width 74- 78 F5.2 0.1nm EWHa H{alpha} equivalent width 80- 84 F5.2 0.1nm e_EWHa H{alpha} equivalent width error 86- 94 E9.4 mW/m2 FHa H{alpha} flux (in erg/cm2/s) 96-104 E9.4 mW/m2 e_FHa H{alpha} flux error (in erg/cm2/s) 107-111 F5.2 --- logRHa logarithm of Luminosity ratio H{alpha}/Bolometric log(L_H{alpha}_/L_bol_) 114-117 F4.2 --- e_logRHa Error of log(L_H{alpha}_/L_bol_) 122-124 A3 --- Sample Sample (1) -------------------------------------------------------------------------------- Note (1): Subsample as follows: C = Cantat Gaudin et al. (2018A&A...618A..93C, Cat. J/A+A/618/A93) H = Hunt & Reffert (2024A&A...686A..42H, Cat. J/A+A/686/A42) Q = Qin et al. (2026ApJ..1002...81Q) -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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) -------------------------------------------------------------------------------- Note (1): Subsample as follows: C = Cantat Gaudin et al. (2018A&A...618A..93C, Cat. J/A+A/618/A93) H = Hunt & Reffert (2024A&A...686A..42H, Cat. J/A+A/686/A42) Q = Qin et al. (2026ApJ..1002...81Q) -------------------------------------------------------------------------------- Byte-by-byte Description of file: tableb2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Note (1): Star name as follows: HD number or LAMOST designation -------------------------------------------------------------------------------- Byte-by-byte Description of file: tableb3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- 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