Red Giant Candidates Research Articles

Spectroscopic identification of rapidly rotating red giant stars in APOKASC-3 and APOGEE DR16

ABSTRACT Rotationally enhanced red giant stars are astrophysically interesting but rare. In this paper, we present a catalogue of 3217 active red giant candidates in the APOGEE DR16 (Apache Point Observatory Galactic Evolution Experiment – Data Release 16) survey. We use a control sample in the well-studied Kepler fields to demonstrate a strong relationship between rotation and anomalies in the spectroscopic solution relative to typical giants. Stars in the full survey with similar solutions are identified as candidates. We use vsini measurements to confirm that 50 ± 1.2 per cent of our DR16 candidates are rotationally enhanced (vsini > 5 km s−1), compared to 4.9 ± 0.2 per cent in the Kepler control sample. In both, the Kepler control sample and a control sample from DR16, we find that there are 3–4 times as many giants rotating with intermediate velocities of 5 < vsini < 10 km s−1 compared to velocities of vsini > 10 km s−1, the traditional threshold for rapid rotation for red giants. The vast majority of intermediate rotators are not spectroscopically anomalous. We use binary diagnostics from APOGEE and Gaia to infer a binary fraction of 73 ± 2.4 per cent among the confirmed rotationally enhanced giants in DR16. We identify a significant bias in the reported metallicity for DR16 candidates with complete spectroscopic solutions, with a median offset of −0.37 dex in [M/H] from a control sample. As such, up to 10 per cent of stars with reported [M/H]<−1 are not truly metal poor. Finally, we use Gaia data to identify a subpopulation of main-sequence photometric binaries erroneously classified as giants.

Red Giants Search Method Based on Convolutional Neural Networks

Red giants play a crucial role in astronomical exploration. However, the current search for these stars heavily relies on spectrum analysis, making it a cumbersome process. In this paper, we propose a novel red giant search approach called CBAMResNets. CBAMResNets enhances feature extraction from images by incorporating the Convolutional Block Attention Module into the ResNets model. To train and validate our model, we utilize accurately labeled stellar image data obtained by combining the Sky Mapper Southern Survey (SMSS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. Our experiments demonstrate that CBAMResNets outperforms other networks such as VGG16 and TPC across most performance metrics and remains competitive with traditional machine-learning methods. Specifically, for stars within the magnitude range of 11–19 in the u band, our model achieves a precision rate of 0.92 and a recall rate of 0.9194. Similarly, for stars within the magnitude range of 11–15 in the u band, the precision rate is 0.92, and the recall rate is 0.9813. Furthermore, we apply CBAMResNets to the SMSS subregion, resulting in the identification of 20,243 potential red giant candidates out of the 304,477 observed stars. We validate the authenticity of these candidates by analyzing their stellar absolute magnitudes and temperatures, estimating a contamination rate of approximately 6.4%. Additionally, we examine the approximate distribution of their metallicity. The catalog containing the identified red giant candidates can be accessed at Zenodo. 4 4 doi:10.5281/zenodo.8352420

Strömgren metallicities for intermediate-age and old star clusters

We report results that show that the straightforward star cluster metallicities obtained from Strömgren vby photometry are age-dependent and need to be corrected for further use. This outcome arises from the comparison of [Fe/H] values derived from Strömgren photometry with those metallicities published in the literature for 26 Large and Small Magellanic Cloud star clusters, whose ages range from ∼1 Gyr up to the oldest-known globular cluster ages in these galaxies. While deriving mean star cluster metallicities, we carried out a thorough selection of red giant branch candidates to comply with the Strömgren metallicity calibration validity regime. We paid attention to the effect of contamination by field stars, particularly those that lie inside the star clusters’ radii, that are distributed along the star cluster red giant branches and that have [Fe/H] values covering a similar range as that for the selected stars. We find that the measured Strömgren metallicities are systematically more metal-poor than the published ones and that a quadratically age-varying function reproduces the relative metallicity values with an overall uncertainty of ∼0.05 dex. We finally performed a similar comparison relying on a fully independent approach, which consisted in using theoretical red giant branches of old globular clusters spanning [Fe/H] values from −2.0 up to 0.0 dex as standards. We then superimposed onto them the red giant branches of star clusters with ages in the range 1.0−12.5 Gyr and estimated their associated metallicities by interpolation. The derived theoretical relative metallicities follow a similar trend as a function of the star clusters’ ages as what has been found from observations of star clusters.

What can Gaia (with Thirty Meter Telescope) say about the Sculptor Dwarf's Core?

Abstract Walker et al.'s Magellan/Michigan/MIKE Fiber System (MMFS) survey identified 1355 red giant candidates in the dwarf spheroidal galaxy Sculptor. We find that the Gaia satellite will be able to measure the proper motions of 139 of these with a precision of between 13 and 20 km s−1. Using a Jeans analysis and 5-parameter density model we show that this allows a determination of the mass within the deprojected half-light radius to within 16 per cent and a measurement of the dark matter density exponent γ to within 0.68 within that radius. If, even at first light, the Thirty Meter Telescope (TMT) observes Sculptor then the combined observations will improve the precision on these proper motions to about 5 km s−1, about 5 years earlier than would be possible without Gaia, further improving the precision of γ to 0.27. Using a bimodal stellar population model for Sculptor the precision of γ improves by about 30 per cent. This suggests that Gaia (with TMT) is capable of excluding a cusped profile of the kind predicted by CDM simulations with 2σ (4σ) of confidence.

CCD [formula omitted] photometry of twenty open clusters

Fundamental astrophysical parameters have been derived for 20 open clusters (OCs) using CCD UBV(RI)C photometric data observed with the 84cm telescope at the San Pedro Mártir National Astronomical Observatory, México.The interstellar reddenings, metallicities, distances, and ages have been compared to the literature values. Significant differences are usually due to the usage of diverse empirical calibrations and differing assumptions, such as concerning cluster metallicity, as well as distinct isochrones which correspond to differing element-abundance ratios, internal stellar physics, and photometric systems. Different interstellar reddenings, as well as varying reduction and cluster-membership techniques, are also responsible for these kinds of systematic differences and errors.The morphological ages, which are derived from the morphological indices (δV and δ1) in the CM diagrams, are in good agreement with the isochrone ages of 12OCs, those with good red clump (RC) and red giant (RG) star candidates. No metal abundance gradient is detected for the range 6.82⩽RGC⩽15.37kpc, nor any correlation between the cluster ages and metal abundances for these 20OCs.Young, metal-poor OCs, observed here in the third Galactic quadrant, may be associated with stellar over-densities, such as that in Canis Major (Martin et al.) and the Monoceros Ring (Newberg et al.), or signatures of past accretion events, as discussed by Yong et al. and Carraro et al.

THE TENTH DATA RELEASE OF THE SLOAN DIGITAL SKY SURVEY: FIRST SPECTROSCOPIC DATA FROM THE SDSS-III APACHE POINT OBSERVATORY GALACTIC EVOLUTION EXPERIMENT

The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents the tenth public data release (DR10) from its current incarnation, SDSS-III. This data release includes the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The APOGEE instrument is a near-infrared R~22,500 300-fiber spectrograph covering 1.514--1.696 microns. The APOGEE survey is studying the chemical abundances and radial velocities of roughly 100,000 red giant star candidates in the bulge, bar, disk, and halo of the Milky Way. DR10 includes 178,397 spectra of 57,454 stars, each typically observed three or more times, from APOGEE. Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included.DR10 also roughly doubles the number of BOSS spectra over those included in the ninth data release. DR10 includes a total of 1,507,954 BOSS spectra, comprising 927,844 galaxy spectra; 182,009 quasar spectra; and 159,327 stellar spectra, selected over 6373.2 square degrees.

STELLAR VELOCITIES IN THE CARINA, FORNAX, SCULPTOR, AND SEXTANS dSph GALAXIES: DATA FROM THE MAGELLAN/MMFS SURVEY

We present spectroscopic data for individual stars observed from 2004 March through 2008 August as part of our Michigan/MIKE Fiber System (MMFS) survey of four dwarf spheroidal (dSph) galaxies: Carina, Fornax, Sculptor, and Sextans. Using MMFS at the Magellan/Clay Telescope at Las Campanas Observatory, we have acquired 8855 spectra from 7103 red-giant candidates in these Galactic satellites. We list measurements of each star's line-of-sight velocity (median error ±2.1 km s–1) and spectral line indices for iron and magnesium absorption features. We use globular cluster spectra to calibrate the indices onto standard [Fe/H] metallicity scales, but comparison of the resulting metallicities with published values suggests that the MMFS indices are best used as indicators of relative, not absolute, metallicity. The empirical distributions of velocity and spectral indices also allow us to quantify the amount of contamination by foreground stars. In a companion paper, we develop an algorithm that evaluates the membership probability for each star, showing that the present MMFS sample contains more than 5000 dSph members, including 774 Carina members, 2483 Fornax members, 1365 Sculptor members, and 441 Sextans members.

Kinematic and Chemical Constraints on the Formation of M31’s Inner and Outer Halo

The halo of M31 shows a wealth of substructures, some of which are consistent with assembly from satellite accretion. Here we report on kinematic and abundance results from Keck DEIMOS spectroscopy in the near-infrared calcium triplet region of over 3500 red giant star candidates along the minor axis and in off-axis spheroid fields of M31. These data reach out to large radial distances of about 160 kpc. The derived radial velocity distributions show an indication of a kinematically cold substructure around ~17 kpc, which has been reported before. We devise a new and improved method to measure spectroscopic metallicities from the calcium triplet in low signal-to-noise ratio spectra using a weighted co-addition of the individual lines. The resulting distribution (accurate to ~0.3 dex down to signal-to-noise ratios of 5) leads us to note an even stronger gradient in the abundance distribution along M31's minor axis and in particular toward the outer halo fields than previously detected. The mean metallicity in the outer fields reaches below –2 dex, with individual values as low as –2.6 dex. This is the first time such a metal-poor halo has been detected in M31. In the fields toward the inner spheroid, we find a sharp decline of ~0.5 dex in metallicity in a region at ~20 kpc, which roughly coincides with the edge of an extended disk, previously detected from star count maps. A large fraction of red giants that we detect in the most distant fields are likely members of M33's overlapping halo. A comparison of our velocities with those predicted by new N-body simulations argues that the event responsible for the Giant Stream is most likely not responsible for the full population of the inner halo. We show further that the abundance distribution of the Stream is different from that of the inner halo, from which it becomes evident, in turn, that the merger event that formed the Stream and the outer halo cannot have contributed any significant material to the inner spheroid. All these severe structure changes in the halo suggest a high degree of infall and stochastic abundance accretion governing the buildup of M31's inner and outer halo.

Photometric membership and metallicities of red giant candidates in selected open clusters

AbstractAs part of a long‐term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high‐precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial‐velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E (B –V) colour excesses were determined from combined B – V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities. The derived DDO metallicities range between values typical of moderately metal‐poor clusters ([Fe/H] = –0.19) to moderately metal‐rich ([Fe/H] = 0.25) ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

NGC 2236: a moderately metal-poor open cluster of Hyades-like age located beyond the Perseus spiral arm

New CCD photometry in the Washington system C and T1 passbands down to T1∼ 18.5 mag in the field of the northern open cluster NGC 2236 is presented. T1 magnitudes and C−T1 colours for a total of 1162 stars within an area of 13.6 × 13.6 arcmin2 were measured. These CCD data were supplemented with photoelectric CMT1T2 photometry of 13 red giant candidates. The comparison of the cluster (T1, C−T1) colour–magnitude diagram with theoretical isochrones computed for the Washington system yields E(C−T1) = 1.10 ± 0.10 and for log t= 8.80 (t= 600+100−40 Myr) and Z= 0.008. The derived E(C−T1) value implies E(B−V) = 0.55 ± 0.05. NGC 2236 is then located at 2.5 ± 0.5 kpc from the Sun beyond the Perseus spiral arm and at ∼10.8 kpc from the Galactic centre. A cluster angular diameter of 9.4 arcmin, equivalent to 6.8 pc, was estimated from star counts both within and outside the cluster field. We also derived from the stellar density profile a cluster core radius of rc= 1.7 arcmin (1.2 pc) and an annular corona of Δrc= 1.8rc (2.2 pc). Five independent Washington abundance indices yield a mean cluster metallicity of [Fe/H]=−0.3 ± 0.2, which is not only in reasonably good agreement with the one obtained from the isochrone fit, but also compatible with the existence of a radial abundance gradient in the Galactic disc. We examined the properties of a sample of 20 known open clusters aligned along the line-of-sight to NGC 2236. Berkeley 27 appears as the farthest and oldest cluster of the studied sample.

CCD BVI photometry and Coravel observations of stars in the open cluster NGC 2489

Abstract We present CCD BVI photometry for the southern open cluster NGC 2489 and its surrounding field. The sample consists of 2182 stars measured in an area of 13.6 × 13.6 arcmin2, extending down to V∼ 21.5. These data are supplemented with CORAVEL radial-velocity observations for seven red giant candidates. A cluster angular radius of 6.7 ± 0.6 arcmin, equivalent to 3.5 ± 0.3 pc, is estimated from star counts carried out inside and outside the cluster region. The comparison of the cluster colour–magnitude diagrams with isochrones of the Padova group yields E(B−V) = 0.30 ± 0.05, E(V−I) = 0.40 ± 0.05 and V−MV= 12.20 ± 0.25 for log t= 8.70 (t= 500+130−100 Myr) and Z= 0.019. NGC 2489 is then located at 1.8 ± 0.3 kpc from the Sun and 25 pc below the Galactic plane. The analysis of the kinematical data allowed us to confirm cluster membership for six red giants, one of them being a spectroscopic binary. A mean radial velocity of 38.13 ± 0.33 km s−1 was derived for the cluster red giants. The properties of a sample of open clusters aligned along the line of sight of NGC 2489 are examined.

Membership, binarity, reddening and metallicity of red giant candidates in three southern open clusters

37 potential members of the red-giant branches of NGC 6192, NGC 6208 and NGC 6268 were observed in the UBV system, while 22 of them were also observed in the DDO system. The observations were made at La Silla and Cerro Tololo Inter-American observatories (Chile), using pulse-counting photoelectric photometers. Coravel radial velocities (RVs) were obtained at La Silla for 24 red giant candidates in the three clusters. Five stars of NGC 6192 have RVs in the narrow range -8.8 km/s < VR < -6.4 km/s, including two new spectroscopic binaries (SBs). Three stars of NGC 6208 – including a new SB – and three stars of NGC 6268 show similar RVs so that their physical membership to NGC 6208 and NGC 6268, respectively, is highly probable. Mean radial velocities are: -7.7 ± 0.38 km/s (NGC 6192), -32.21 ± 0.28 km/s (NGC 6208) and -15.11 ± 0.08 km/s (NGC 6268). We have also derived the following mean E(B-V) values from Janes (1977) iterative method: 0.63 ± 0.02 (NGC 6192), 0.31 ± 0.02 (NGC 6208) and 0.43 ± 0.02 (NGC 6268).

Photometric and Coravel observations of red giant candidates in three open clusters: membership, binarity, reddening and metallicity

Aims. We present new CORAVEL radial-velocity observations and photoelectric photometry in the UBV and DDO systems for a sample of potential members of the red-giant branches of NGC 6192, NGC 6208 and NGC 6268, three open clusters projected close to the Galactic center direction. We also examine the properties of a sample of 42 inner disk open clusters projected towards almost the same direction as the three clusters. Methods. Cluster members and red field giants were discriminated by using the CORAVEL radial-velocity data and by applying two photometric criteria. Interstellar reddening and metal content of the clusters were derived from combined BV and DDO data. Results. Cluster membership for five red giants in NGC 6192, three in NGC 6208 and three in NGC 6268 has been confirmed by the analysis of the photometric and kinematic data. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. Three new spectroscopic binaries were discovered among the red giants of NGC 6192 and NGC 6208. Mean radial velocities and E(B − V) colour excesses were derived. Conclusions. The overall metallicities were found to be nearly solar for NGC 6208 and above solar for NGC 6192 and NGC 6268. Most of the clusters located closer than 2 kpc from the Sun in the considered direction are slightly more reddened than the absorption resulting from the Baade’s window absorption law.

Washington photometry of open cluster giants: two moderately metal-poor anticentre clusters

New photometric data in the Washington system are presented for red giant candidates in NGC 1817 and 2251, two open clusters located towards the Galactic anticentre direction. In the case of NGC 2251, the Washington data are supplemented with new UBV and David Dunlap Observatory (DDO) photoelectric photometry. Published radial velocities are used to separate field stars from cluster giants. The photometric data yield an effective temperature and metal abundance for each cluster member. Five independent Washington abundance indices yield mean metallicities of [Fe/H] = 0.25 ± 0.04 for NGC 1817 and 2251, respectively. From combined BV and DDO data, we also derive E(B − V ) = 0.21 ± 0.03 and [Fe/H]DDO = −0.14 ± 0.05 for NGC 2251. Both objects are then found to be on the metal-poor side of the distribution of open clusters, their metallicities being compatible with the existence of a radial abundance gradient in the disc. Using the WEBDA Open Cluster data base and the available literature, we re-examined the overall properties of a sample of 30 clusters located towards the Galactic anticentre with the distances, ages and metallicities available. This cluster sample presents no evidence of an abundance gradient perpendicular to the Galactic plane, nor is an age‐metallicity relation found. However, a radial abundance gradient of −0.093 dex kpc −1 is derived over a Galactocentric distance of 14 kpc, a gradient which is in keeping with most recent determinations. This value practically does not change when all clusters with basic parameters known up to this date are considered. Ke yw ords: methods: observational ‐ techniques: photometric ‐ open clusters and associations: individual: NGC 1817 ‐ open clusters and associations: individual: NGC 2251 ‐ Galaxy: abundances.

New neighbours

We present spectra of 36 nearby star candidates and 3 red giant candidates, identified in the DENIS database. 32 of the dwarf candidates are nearby red dwarfs, with spectral types from M 5.5 to M 8.5. Out of 11 targets with low proper motion ( µ< 0. 1a rcsec yr −1 ) but a Reduced Proper Motion above an inclusive threshold, 9 are red dwarfs. The 4 contaminants are all reddened F-K main sequence stars, and could have been eliminated by checking for small well-known high latitude molecular clouds. These stars might be of interest as probes of interstellar absorption. For the red dwarfs we derive spectral types and spectroscopic distances, using a new calibration of the PC3 spectral index to absolute magnitudes in the I, J, H and K photometric bands. We confirm 2 new members of the 12 pc volume (2 new M 8.5), and one M 7.5 NLTT object closer than 10 pc; and show that one quarter of the stars with photometric distances under 30 pc have too small a proper motion for inclusion in the NLTT catalog.

Absolute Proper Motion of the Sagittarius Dwarf Galaxy and of the Outer Regions of the Milky Way Bulge

We have determined the absolute proper motion of the Sagittarius dwarf spheroidal galaxy (Sgr) from the Southern Proper Motion Catalog 3, by selecting red giant candidates from the Two Micron All Sky Survey. We obtain μl cos b = -2.35 ± 0.20 and μb = 2.07 ± 0.20 mas yr-1. Using the same procedure, we also determine the absolute proper motion of the bulge in the region of the sky that overlaps with Sgr. For the bulge, we obtain μl cos b = -5.86 ± 0.14 and μb = -0.59 ± 0.14 mas yr-1, at l = 76 and b = -212. The absolute proper motions are on the International Celestial Reference System via Hipparcos Catalog stars.

Red giants in open clusters

New, accurate radial velocities and photoelectric ${\it UBV}$ photometry of 83 red-giant candidates in the field of the rich, intermediate-age open cluster NGC 2477 ($\rm [Fe/H]= -0.05$, $\rm age \simeq1$ Gyr) are presented and discussed. From 49 constant-velocity members we find a mean cluster velocity of $+7.32\pm0.13$ km s -1 and confirm the membership of 76 of the stars. Among the cluster members, we identify 26 definite and 1 probable spectroscopic binaries and determine orbits for 13 of these systems, with periods ranging from 40 to 4578 days. The binary frequency is thus rather high ($27/76 = 36\%$). The observed internal radial velocity dispersion of the cluster, as determined from the single member stars, is 0.93 km s -1 , corrected for the small average observational error of 0.22 km s -1 . Fitting King-type models to the observed stellar density distribution and velocity dispersion, and assuming a distance of 1.25 kpc, we find the core and tidal radii of NGC 2477 to be 1.8 and 8.1 pc, respectively, and estimate that the mass of cluster stars down to $V = 17$, corresponding to ~$1~M_{\odot}$, is at least 5400 $M_{\odot}$. The substantial differential reddening of NGC 2477 requires a more detailed study before definitive isochrone fits can be made.

The relatively young and metal-poor Galactic open cluster NGC 2194

We present CCD VIKC photometry down to V≈ 21 mag in the field of the rich open cluster NGC 2194, which is projected towards the Galactic anticentre direction. We measured V magnitudes and V−I colours for a total of 2515 stars in a field of 13.6 × 13.6 arcmin2. These data are supplemented with CCD photometry in the C, M and T1 filters of the Washington system and photoelectric CMT1T2 photometry of 20 red giant candidates. Based on the best fits of isochrones computed by the Geneva and Padova groups to the (V, V−I) colour — magnitude diagram, we derive a colour excess E(V−I) = 0.75, a cluster distance of 3.2 kpc and an age of 400 Myr. Five independent Washington abundance indices yield a mean cluster metallicity of [Fe/H]=−0.27 ± 0.06, which is compatible with the existence of both a radial and Z gradient in the Galactic disc. NGC 2194 is a relatively young open cluster, whose deficiency in metal content can be accounted for by the fact that it was born not only far from the Galactic centre in the outer disc, but also at a relatively high Z value.

Multicolour photometry and Coravel observations of stars in the southern open cluster IC 2488

We present new UBV photoelectric observations of 119 stars in the field of the southern open cluster IC 2488, supplemented by DDO and Washington photometry and Coravel radial velocities for a sample of red giant candidates. Nearly 50% of the stars sampled - including three red giants and one blue straggler - are found to be probable cluster members. Photometric membership probabilities of the red giant candidates show good agreement with those obtained from Coravel data. A mean radial velocity of ( 2.63 0.06) km s 1 is derived for the cluster giants. The reddening across the cluster is found to be uniform, the mean value being E(B V)= 0.24 0.04. IC 2488, located at a distance of (1250 120) pc from the Sun and 96 pc below the Galactic plane, is most probably not related to the planetary nebula ESO 166-PN21. A metal abundance (Fe/H)= 0.10 0.06 relative to the Sun is determined from DDO data of the red giant members, in good agreement with the (Fe/H) values derived from five independent Washington abundance indices. An age of 180 Myr is determined from the fitting of isochrones computed with convective overshooting for Z = 0.019. The isochrone for log t= 8.25 reproduces remarkably well not only the morphology of the upper main sequence but also the observed red giant pattern.

Red giants in open clusters

Radial-velocity and BV CCD observations of 29 red-giant candidates in the central part of the intermediate-age open cluster NGC 1817 have confirmed the membership of 21 stars. In addition, we have used radial velocities and new UBVR photoelectric photometry to investigate the membership of 59 new candidates located in an outer corona surrounding NGC 1817, identified from the POSS plates. We have confirmed 18 new members out to a distance of 27′ from the centre, thus doubling the previous cluster radius. Ten definite spectroscopic-binary members have been discovered, corresponding to a binary frequency of 25.6% and four orbits have been determined so far. Three additional stars have been identified as possible spectroscopic-binary members. We derive a cluster mean velocity of +65.33 ± 0.09 (0.52 s.e.) km s-1 based on 29 members with no detected velocity variations plus the 3 binary members with orbital solutions. The radial distribution of the 39 red-giant members shows a strong concentration of spectroscopic binaries in the inner part of the cluster, similar to that observed in M 67, although NGC 1817 is much younger.