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Start Over Subject open star clusters Publisher CDS
691. NGC 1817 proper motions and membership
ID:
ivo://CDS.VizieR/J/A+A/426/819
Title:
NGC 1817 proper motions and membership
Short Name:
J/A+A/426/819
Date:
21 Oct 2021
Publisher:
CDS
Description:
Absolute proper motions, their errors and membership probabilities of 810 stars in the area of two NGC objects, NGC 1817 and NGC 1807. The Tycho-2 Catalogue is used as the reference frame, and the cross-identification is given. Parametric and non parametric membership probabilities are compared based on there being only one very extended physical cluster: NGC 1817.
692. NGC 7789 radial velocities
ID:
ivo://CDS.VizieR/J/PASP/110/1172
Title:
NGC 7789 radial velocities
Short Name:
J/PASP/110/1172
Date:
21 Oct 2021
Publisher:
CDS
Description:
A total of 597 radial velocity observations for 112 stars in the ~1.6Gyr old open cluster NGC 7789 have been obtained since 1979 with the radial velocity spectrometer at the Dominion Astrophysical Observatory. The mean cluster radial velocity is -54.9+/-0.12km/s and the dispersion is 0.86km/s, from 50 constant velocity stars selected as members from this radial velocity study and the 1981 proper motion study of McNamara & Solomon (1981A&AS...43..337M). Twenty-five stars (32%) among 78 members are possible radial velocity variable stars, but no orbits are determined because of the sparse sampling. Seventeen stars are radial velocity nonmembers, while the membership estimates of six stars are uncertain. There is a hint that the observed velocity dispersion falls off at large radius: this may be due to the inclusion of long-period binaries preferentially in the central area of the cluster. The known radial velocity variables also seem to be more concentrated toward the center than members with constant velocity. Although this is significant at only the 85% level, when combined with the similar result of Raboud & Mermilliod (1994A&A...289..121R) for three other clusters, the data strongly support the conclusion that mass segregation is being detected.
693. NGC 2354 red giants
ID:
ivo://CDS.VizieR/J/A+AS/134/301
Title:
NGC 2354 red giants
Short Name:
J/A+AS/134/301
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new Coravel radial-velocity observations and photoelectric photometry in the UBV, DDO and Washington systems for a sample of red giant candidates in the field of the intermediate-age open cluster NGC 2354. Photometric membership probabilities show very good agreement with those obtained from Coravel radial velocities. The analysis of the photometric and kinematical data allow us to confirm cluster membership for 9 red giants, one of them being a spectroscopic binary, while 4 confirmed spectroscopic binaries appear to be probable members. We have also discovered 4 spectroscopic binaries not belonging to the cluster. A mean radial velocity of (33.40+/-0.27)km/s and a mean reddening E(B-V)=0.13+/-0.03 were derived for the cluster giants. NGC 2354 has a mean ultraviolet excess <{delta}(U-B)>=-0.03+/-0.01, relative to the field K giants, and a mean new cyanogen anomaly {Delta}CN=-0.035+/-0.007, both implying [Fe/H]=~-0.3. The moderately metal-poor character of NGC 2354 is confirmed using five different metal abundance indicators of the Washington system. The cluster giant branch is formed by a well defined clump of 7 stars and 4 stars with high membership probabilities seem to define an ascending giant branch. The whole red giant locus cannot be reproduced by any theoretical track.
694. NGC 1960 (RI)c photometric catalogue
ID:
ivo://CDS.VizieR/J/MNRAS/434/2438
Title:
NGC 1960 (RI)c photometric catalogue
Short Name:
J/MNRAS/434/2438
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a deep Cousins RI photometric survey of the open cluster NGC 1960, complete to R_C_=~22, I_C_=~21, that is used to select a sample of very low mass cluster candidates. Gemini spectroscopy of a subset of these is used to confirm membership and locate the age-dependent 'lithium depletion boundary' (LDB) - the luminosity at which lithium remains unburned in its low-mass stars. The LDB implies a cluster age of 22+/-4Myr and is quite insensitive to choice of evolutionary model. NGC 1960 is the youngest cluster for which a LDB age has been estimated and possesses a well-populated upper main sequence and a rich low-mass pre-main sequence. The LDB age determined here agrees well with precise age estimates made for the same cluster based on isochrone fits to its high- and low-mass populations. The concordance between these three age estimation techniques, that rely on different facets of stellar astrophysics at very different masses, is an important step towards calibrating the absolute ages of young open clusters and lends confidence to ages determined using any one of them.
695. NGC 330 seen by MUSE
ID:
ivo://CDS.VizieR/J/A+A/634/A51
Title:
NGC 330 seen by MUSE
Short Name:
J/A+A/634/A51
Date:
21 Oct 2021
Publisher:
CDS
Description:
A majority of massive stars are part of binary systems, a large fraction of which will inevitably interact during their lives. Binary-interaction products (BiPs), i.e. stars affected by such interaction, are expected to be commonly present in stellar populations. BiPs are thus a crucial ingredient in the understanding of stellar evolution. We aim to identify and characterize a statistically significant sample of BiPs by studying clusters of 10-40Myr, an age at which binary population models predict the abundance of BiPs to be highest. One example of such a cluster is NGC 330 in the Small Magellanic Cloud. Using MUSE WFM-AO observations of NGC 330, we resolve the dense cluster core for the first time and are able to extract spectra of its entire massive star population. We develop an automated spectral classification scheme based on the equivalent widths of spectral lines in the red part of the spectrum. We characterize the massive star content of the core of NGC 330 which contains more than 200 B stars, 2 O stars, 6 A-type supergiants and 11 red supergiants. We find a lower limit on the Be star fraction of 32+/-3% in the whole sample. It increases to at least 46+/-10% when only considering stars brighter than V=17mag. We estimate an age of the cluster core between 35 and 40Myr and a total cluster mass of 88^+17^_-18_*10^3M_{sun}_. We find that the population in the cluster core is different than the population in the outskirts: while the stellar content in the core appears to be older than the stars in the outskirts, the Be star fraction and the observed binary fraction are significantly higher. Furthermore, we detect several BiP candidates that will be subject of future studies.
696. NGC 330 seen by MUSE. II.
ID:
ivo://CDS.VizieR/J/A+A/652/A70
Title:
NGC 330 seen by MUSE. II.
Short Name:
J/A+A/652/A70
Date:
22 Feb 2022
Publisher:
CDS
Description:
Observations of massive stars in open clusters younger than 8 Myr have shown that a majority of them are in binary systems, most of which will interact during their life. While these can be used as a proxy of the initial multiplicity properties, studying populations of massive stars older than ~20Myr allows us to probe the outcome of such interactions after a significant number of systems have experienced mass and angular momentum transfer and possibly even merged. Using multi-epoch integral-field spectroscopy, we aim to investigate the multiplicity properties of the massive-star population in the dense core of the ~40Myr-old cluster NGC 330 in the Small Magellanic Cloud in order to search for possible imprints of stellar evolution on the multiplicity properties. We obtained six epochs of VLT/MUSE observations operated in wide-field mode with the extended wavelength setup and supported by adaptive optics.We extract spectra and measure radial velocities for stars brighter than m_F814W_=19. We identify single-lined spectroscopic binaries through significant RV variability with a peak-to-peak amplitude larger than 20km/s. We also identify double-lined spectroscopic binaries, and quantify the observational biases for binary detection. In particular, we take into account that binary systems with similar line strength are difficult to detect in our data set. The observed spectroscopic binary fraction among the stars brighter than m_F814W_=19 (~5.5M_{sun}_ on the main sequence) is f^obs^_SB_=13.2+/-2:0%. Considering period and mass ratio ranges from log(P)=0.15-3.5 (about 1.4 to 3160d), and q=0.1-1.0, and a representative set of orbital parameter distributions, we find a bias-corrected close binary fraction of f_cl_=34^+8^_-7_%. This fraction seems to decline for the fainter stars, which indicates either that the close binary fraction drops in the B-type domain, or that the period distribution becomes more heavily weighted towards longer orbital periods.We further find that both fractions vary strongly in different regions of the color-magnitude diagram that corresponds to different evolutionary stages. This probably reveals the imprint of the binary history of different groups of stars. In particular, we find that the observed spectroscopic binary fraction of Be stars (f^obs^_SB_=2+/-2%) is significantly lower than the one of B-type stars (f^obs^_SB_=9+/-2%). In this work we provide the first homogeneous RV study of a large sample of B-type stars at a low metallicity ([Fe/H]<~-1.0). The overall bias-corrected close binary fraction (log(P)<3.5d) of the B-star population in NGC 330 is lower than the one reported for younger Galactic and LMC clusters in previous works. More data are, however, needed to establish whether the observed differences result from an age or a metallicity effect.
697. NGC 6067 stars
ID:
ivo://CDS.VizieR/J/MNRAS/469/1330
Title:
NGC 6067 stars
Short Name:
J/MNRAS/469/1330
Date:
21 Oct 2021
Publisher:
CDS
Description:
NGC 6067 is a young open cluster hosting the largest population of evolved stars among known Milky Way clusters in the 50-150Ma age range. It thus represents the best laboratory in our Galaxy to constrain the evolutionary tracks of 5-7M_{sun}_ stars. We have used high-resolution spectra of a large sample of bright cluster members (45), combined with archival photometry, to obtain accurate parameters for the cluster as well as stellar atmospheric parameters. We derive a distance of 1.78+/-0.12 kpc, an age of 90+/-20Ma and a tidal radius of 14.8^+6.8^_-3.2_ arcmin. We estimate an initial mass above 5700M_{sun}_, for a present-day evolved population of two Cepheids, two A supergiants and 12 red giants with masses ~=6M_{sun}_. We also determine chemical abundances of Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y and Ba for the red clump stars. We find a supersolar metallicity, [Fe/H]=+0.19+/-0.05, and a homogeneous chemical composition, consistent with the Galactic metallicity gradient. The presence of a Li-rich red giant, star 276 with A(Li)=2.41, is also detected. An overabundance of Ba is found, supporting the enhanced s-process. The ratio of yellow to red giants is much smaller than 1, in agreement with models with moderate overshooting, but the properties of the cluster Cepheids do not seem consistent with current Padova models for supersolar metallicity.
698. NGC 3532 stars cChromospheric activity
ID:
ivo://CDS.VizieR/J/A+A/656/A103
Title:
NGC 3532 stars cChromospheric activity
Short Name:
J/A+A/656/A103
Date:
22 Feb 2022
Publisher:
CDS
Description:
The coeval stars of young open clusters provide insights into the formation of the rotation-activity relationship that elude studies of multi-age field populations. We measure the chromospheric activity of cool stars in the 300 Myr old open cluster NGC 3532 in concert with their rotation periods to study the mass-dependent morphology of activity for this transitional coeval population. Using multi-object spectra of the Ca II infrared triplet region obtained with the AAOmega spectrograph at the 4m Anglo- Australian Telescope, we measure the chromospheric emission ratios R'_IRT_ for 454 FGKM cluster members of NGC3532. The morphology of activity against colour appears to be a near-mirror image of the cluster's rotational behaviour. In particular, we identify a group of 'desaturated transitional rotators' that branches off from the main group of unsaturated FGK slow rotators, and from which it is separated by an 'activity gap'. The few desaturated gap stars are identical to the ones in the rotational gap. Nevertheless, the rotation-activity diagram is completely normal. In fact, the relationship is so tight that it allows us to predict rotation periods for many additional stars. We then precisely determine these periods from our photometric light curves, allowing us to construct an enhanced colour-period diagram that represents 66% of the members in our sample. Our activity measurements show that all fast rotators of near-solar mass (F-G type) have evolved to become slow rotators, demonstrating that the absence of fast rotators in a colour-period diagram is not a detection issue but an astrophysical fact. We also identify a new population of low-activity stars among the early Mdwarfs, enabling us to populate the extended slow rotator sequence in the colour-period diagram. The joint analysis of chromospheric activity and photometric time series data thus enables comprehensive insights into the evolution of the rotation and activity of stars during the transitional phase between the Pleiades and Hyades ages.
699. NGC 6253 stars equivalent widths
ID:
ivo://CDS.VizieR/J/AJ/139/2034
Title:
NGC 6253 stars equivalent widths
Short Name:
J/AJ/139/2034
Date:
21 Oct 2021
Publisher:
CDS
Description:
High-dispersion spectra of 89 potential members of the old, super-metal-rich open cluster, NGC 6253, have been obtained with the HYDRA multi-object spectrograph. Based upon radial-velocity measurements alone, 47 stars at the turnoff of the cluster color-magnitude diagram (CMD) and 18 giants are identified as potential members.
700. NGC 6819 stellar radial-velocity and photometry
ID:
ivo://CDS.VizieR/J/AJ/138/159
Title:
NGC 6819 stellar radial-velocity and photometry
Short Name:
J/AJ/138/159
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the current results from our ongoing radial-velocity (RV) survey of the intermediate-age (2.4Gyr) open cluster NGC 6819. Using both newly observed and other available photometry and astrometry, we define a primary target sample of 1454 stars that includes main-sequence, subgiant, giant, and blue straggler stars, spanning a magnitude range of 11<=V<=16.5 and an approximate mass range of 1.1-1.6M_{sun}_. Our sample covers a 23 arcminute (13pc) square field of view centered on the cluster. We have measured 6571 radial velocities for an unbiased sample of 1207 stars in the direction of the open cluster NGC 6819, with a single-measurement precision of 0.4km/s for most narrow-lined stars. We use our RV data to calculate membership probabilities for stars with >=3 measurements, providing the first comprehensive membership study of the cluster core that includes stars from the giant branch through the upper main sequence. We identify 480 cluster members. Additionally, we identify velocity-variable systems, all of which are likely hard binaries that dynamically power the cluster.

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