Coma Berenices Open Cluster Research Articles

A Metallicity Study of F, G, K, and M Dwarfs in the Coma Berenices Open Cluster from the APOGEE Survey

Abstract We present a study of metallicities in a sample of main-sequence stars with spectral types M, K, G, and F (T eff ∼3200–6500K and log g ∼ 4.3–5.0 dex) belonging to the solar neighborhood young open cluster Coma Berenices. Metallicities were determined using the high-resolution (R = λ/Δ λ ∼ 22,500) NIR spectra (λ1.51–λ1.69 μm) of the Sloan Digital Sky Survey IV APOGEE survey. Membership to the cluster was confirmed using previous studies in the literature along with APOGEE radial velocities and Gaia DR2. An LTE analysis using plane-parallel MARCS model atmospheres and the APOGEE DR16 line list was adopted to compute synthetic spectra and derive atmospheric parameters (T eff and log g) for the M dwarfs and metallicities for the sample. The derived metallicities are near-solar and are homogeneous at the level of the expected uncertainties, in particular when considering stars from a given stellar class. The mean metallicity computed for the sample of G, K, and M dwarfs is 〈[Fe/H]〉 = +0.04 ± 0.02 dex; however, the metallicities of the F-type stars are slightly lower, by about 0.04 dex, when compared to cooler and less massive members. Models of atomic diffusion can explain this modest abundance dip for the F dwarfs, indicating that atomic diffusion operates in Coma Berenices stars. The [Fe/H] dip occurs in nearly the same effective temperature range as that found in previous analyses of the lithium and beryllium abundances in Coma Berenices.

The Evolutionary Status of 17 Com, The Hottest Member of Coma Berenices

Abstract The integrated flux, linear radius and effective temperature of 17 Com A (A0p CrEu), the hottest member of the Coma Berenices open cluster, are determined using the Infrared Flux Method. The surface gravity is derived by fitting the H β profile. The effective temperature and surface gravity are found to be smaller than most previous determinations. The evolutionary status of 17 Com A is discussed in light of these new parameters using stellar evolution modeling. 17 Com A appears to be finishing its lifetime on the Main Sequence.

Searching for short-period variable stars in the direction of Coma Berenices and Upgren 1 open clusters: Melotte 111 AV 1224 a new eclipsing binary star

We report the results of CCD photometric observations in the direction of the Coma Berenices and Upgren 1 open clusters with the aim at searching for new short-period variable stars. A total of 35 stars were checked for variability. As a result of this search the star designated in the SIMBAD database as Melotte 111 AV 1224 was found to be a new eclipsing binary star. Follow-up Strömgren photometric and spectroscopic observations allowed us to derive the spectral type, distance, reddening and effective temperature of the star. A preliminary analysis of the binary light curve was performed and the parameters of the orbital system were derived. From the derived physical parameters we conclude that Melotte 111 AV 1224 is most likely a W-UMa eclipsing binary that is not a member of the Coma Berenices open cluster. On other hand, we did not find evidence of brightness variations in the stars NSV 5612 and NSV 5615 previously catalogued as variable stars in Coma Berenices open cluster.

Characterizing the variability of Melotte 111 AV 1224: a new variable star in the Coma Berenices open cluster

AbstractA search for new pulsating stars in the Coma Berenices open cluster was carried out. As a result of this search, the cluster member Melotte 111 AV 1224 presented clear indications of photometric variability. In order to determine its physical parameters, Strömgren standard indices and low-resolution spectra were acquired. In this work, we present the preliminary results of these observations.

The mass function of the Coma Berenices open cluster below 0.2 M⊙: a search for low-mass stellar and substellar members

Context. Little is known about the population of the Coma Berenices open cluster (age ~ 500 Myr) below 0.2 M ⊙ , and statistics show that there is a prominent deficit of very low-mass objects in this mass range compared to younger open clusters with ages of We search for very low-mass stars and substellar objects (brown dwarfs) in the Coma open cluster to derive the present-day cluster mass function below 0.2 M ⊙ .Methods. An imaging survey of the Coma open cluster in the R - and I -bands was carried out with the 2k × 2k CCD Schmidt camera at the 2-m telescope in Tautenburg. We performed a photometric selection of the cluster member candidates by combining results of our survey with 2MASS JHK s photometry. We also analysed low-resolution optical spectroscopic observations of a sample of 14 of our stellar cluster member candidates to estimate their spectral types and luminosity.Results. We present a photometric survey covering 22.5 deg2 around the Coma open cluster centre with a completeness limit of in the R -band and in the I -band. Using optical/IR colour − magnitude diagrams, we identify 82 very low-mass cluster member candidates in the magnitude range . Five of them have luminosities and colour indices consistent with brown dwarfs. We calculate a mass spectrum of the very low-mass end of the cluster under the assumption that all selected candidates are probable cluster members. The calculated present-day mass function (dN /dm ≈ m − α ) can be divided into two parts with a slope of α = 0.6 in the mass interval 0.2 > M ⋆ > 0.14 M ⊙ and α ~ 0 in 0.14 > M ⋆ > 0.06 M ⊙ .Conclusions. Our analysis of the spectroscopy of 14 objects shows that they are very low-mass MV-dwarfs of spectral type and luminosity consistent with Coma open cluster membership. This suggests that the membership probability of our other candidates may be high. Our results suggest that the mass function of the Coma open cluster can be traced towards substellar objects, but comparison with a mass spectra of younger clusters indicates that the Coma open cluster has probably lost its lowest mass members by means of dynamical evolution.

The main-sequence rotation���colour relation in the Coma Berenices open cluster

We present the results of a photometric survey of rotation rates in the Coma Berenices (Melotte 111) open cluster, using data obtained as part of the SuperWASP exoplanetary transit-search programme. The goal of the Coma survey was to measure precise rotation periods for main-sequence F, G and K dwarfs in this intermediate-age (~600 Myr) cluster, and to determine the extent to which magnetic braking has caused the stellar spin periods to converge. We find a tight, almost linear relationship between rotation period and J-K colour with a root-mean square scatter of only 2 percent. The relation is similar to that seen among F, G and K stars in the Hyades. Such strong convergence can only be explained if angular momentum is not at present being transferred from a reservoir in the deep stellar interiors to the surface layers. We conclude that the coupling timescale for angular momentum transport from a rapidly-spinning radiative core to the outer convective zone must be substantially shorter than the cluster age, and that from the age of Coma onward, stars rotate effectively as solid bodies. The existence of a tight relationship between stellar mass and rotation period at a given age supports the use of stellar rotation period as an age indicator in F, G and K stars of Hyades age and older. We demonstrate that individual stellar ages can be determined within the Coma population with an internal precision of order 9 percent (RMS), using a standard magnetic braking law in which rotation period increases with the square root of stellar age. We find that a slight modification to the magnetic-braking power law, P proportional to t^0.56, yields rotational and asteroseismological ages in good agreement for the Sun and other stars of solar age for which p-mode studies and photometric rotation periods have been published.

A massive white dwarf member of the Coma Berenices open cluster

We report the identification, from a photometric, astrometric and spectroscopic study, of a massive white dwarf member of the nearby, approximately solar metalicity, Coma Berenices open star cluster (Melotte 111). We find the optical to near-IR energy distribution of WD1216+260 to be entirely consistent with that of an isolated DA and determine the effective temperature and surface gravity of this object to be $T_{\rm eff}$=$15739^{+197}_{-196}$K and log $g$=$8.46^{+0.03}_{-0.02}$. We set tight limits on the mass of a putative cool companion, M$\simgreat$0.036M$_{\odot}$ (spatially unresolved) and M$\simgreat$0.034M$_{\odot}$, (spatially resolved and a$\simless$2500AU). Based on the predictions of CO core, thick-H layer evolutionary models we determine the mass and cooling time of WD1216+260 to be M$_{\rm WD}$=$0.90 \pm0.04$M$_{\odot}$ and $\tau$$_{\rm cool}$=$363^{+46}_{-41}$Myrs respectively. For an adopted cluster age of $\tau$=500$\pm$100Myrs we infer the mass of its progenitor star to be M$_{\rm init}$=$4.77^{+5.37}_{-0.97}$M$_{\odot}$. We briefly discuss this result in the context of the form of the stellar initial mass-final mass relation.

Chemical composition of A and F dwarf members of the Coma Berenices open cluster

Aims. Abundances of 18 chemical elements have been derived for 11 A (normal and Am) and 11 F dwarfs members of the Coma Berenices open cluster in order to set constraints on evolutionary models including transport processes (radiative and turbulent diffusion) calculated with the Montreal code. Methods. A spectral synthesis iterative procedure has been applied to derive the abundances from selected high quality lines in high resolution high signal-to-noise echelle spectra obtained with ELODIE at the Observatoire de Haute Provence. Results. The chemical pattern found for the A and F dwarfs in Coma Berenices is reminiscent of that found in the Hyades and the UMa moving group. In graphs representing the abundances [X/H] versus the effective temperature, the A stars often display abundances much more scattered around their mean values than the F stars do. Large star-to-star variations are detected for A stars in their abundances of C, O, Na, Sc, Ti, Mn, Fe, Ni, Sr, Y, Zr and Ba which we interpret as evidence of transport processes competing with radiative diffusion. The abundances of Mn, Ni, Sr and Ba are strongly correlated with that of iron for A and Am stars. In contrast the ratios [C/Fe] and [O/Fe] appear to be anticorrelated with [Fe/H] as found earlier for field A dwarfs. All Am stars in Coma Berenices are deficient in C and O and overabundant in elements heavier than Fe but not all are deficient in calcium and/or scandium. The F stars have solar abundances for almost all elements except for Mg, Si, V and Ba. The derived abundances patterns, [X/H] versus atomic number, for the slow rotator HD 108642 (A2m) and the moderately fast rotator HD 106887 (A4m) were compared to the predictions of self consistent evolutionary model codes including radiative and different amounts of turbulent diffusion. None of the models reproduces entirely the overall shape of the abundance pattern. Conclusions. While part of the discrepancies between derived and predicted abundances may be accounted for by non-LTE effects, the inclusion of competing processes such as rotational mixing in the radiative zones of these stars seems necessary to improve the agreement between observed and predicted abundance patterns.

New stellar and substellar candidate members of the Coma Berenices open star cluster

AbstractWe present the results of a survey of the open star cluster Melotte 111 in Coma Berenices, undertaken using the USNO‐B1.0 and 2MASS Point Source catalogues. On the basis of their astrometric and photometric properties, we have identified 60 new candidate members with masses in the range 1.007 < M < 0.269 M⊙. We estimate a membership probability for each by extracting control clusters from the proper motion vector diagram. All 60 are found to have greater than 60 per cent probability of being cluster members, which if they are confirmed as members, more than doubles the number of known cluster members. We also have I and Z photometry for 100 low mass candidate members of the cluster, 13 of which we suggest may be brown dwarfs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

New stellar members of the Coma Berenices open star cluster

We present the results of a survey of the Coma Berenices open star cluster (Melotte 111), undertaken using proper motions from the USNO-B1.0 (United States Naval Observatory) and photometry from the Two-Micron All-Sky Survey (2MASS) Point Source catalogues. We have identified 60 new candidate members with masses in the range 1.007 < M < 0.269 M⊙. For each we have estimated a membership probability by extracting control clusters from the proper motion vector diagram. All 60 are found to have greater than 60 per cent probability of being members, more than doubling the number of known cluster members. The new luminosity function for the cluster peaks at bright magnitudes, but is rising at K≈ 12, indicating that it is likely that lower mass members may exist. The mass function also supports this hypothesis.

Lithium in the Coma Berenices open cluster

Lithium abundances, radial velocities, and rotational velocities are reported for 20 candidate F, G and K stars of the sparse Coma Berenices open cluster. All the stars are proper-motion selected, and our radial velocities support the membership credentials of at least 12 of the candidates. Combining our data with that in the literature, we have a close-to-complete census of Li abundances for late-type stars with MV < 5:8. These data show that the Li-depletion pattern in Coma Ber is similar, but not identical, to that in the Hyades cluster, which has a similar age but higher metallicity. Several Coma Ber F stars have suered signicantly more Li depletion than their counterparts in the Hyades. The G and early-K stars of Coma Ber have undergone less Li depletion than those of the Hyades, but much more than that predicted by standard evolutionary models featuring only convective mixing. This provides strong evidence for additional mixing and Li depletion operating in these stars during their rst 400 Myr on the main sequence, amounting to 0.3 dex at 6000 K and rising to 0.8{1.2 dex at 5400 K. We nd that 4 of the radial-velocity non-members are among a small number of low-mass stars which were previously reported as part of an extra-tidal moving group associated with the Coma Ber cluster. As a result, we now nd that the luminosity function of this moving group is indistinguishable from that of the central cluster. It is uncertain whether there may be a signicant number of stars with even lower masses among the moving group.

Lithium in the low-mass stars of the Coma Berenices open cluster

ABSTRA C T I report lithium abundances and radial velocities for 15 late F, G and K stars in the Coma Berenices open cluster. All the stars are proper motion members, and the radial velocities enable us to confirm membership for 11 single stars and identify three SB1 systems and one short-period SB2 system that are very probable cluster members. The pattern of Li abundances is similar to that in the Hyades, with some evidence for higher Li abundances in Coma Ber for Teff < 5700 K. I argue that these data do not support standard models for Li depletion involving only convective mixing, because the Coma Ber stars have consistently determined lower metallicities and shallower convection zones than the Hyades and should have suffered a great deal less Li depletion than observed. Instead, it seems that the Li abundances in these and other young clusters are primarily ranked according to their age rather than their metallicity. I propose a scenario where the extreme metallicity dependence of pre-main-sequence Li depletion is tempered by a mechanism that severely inhibits convective mixing, where continued main-sequence depletion occurs via non-standard mixing mechanisms, and where any dependence of Li depletion on metallicity takes at least several hundred Myr to emerge.

FAUST observations of ultraviolet sources in the direction of Coma

We analyse an ultraviolet observation toward the Coma cluster by means of the FAUST shuttle-borne telescope. We detect 56 candidate sources to a signal-to-noise ratio of 6.5. Most sources have optical counterparts in existing catalogues and are stars. 10 sources with no listed counterparts were observed at the Wise Observatory. We present identifications based on low-resolution spectrophotometry, and discuss the foreground stars and the galaxies, all in the foreground of the Coma cluster. The FAUST image yields a higher fraction of hot evolved stars than either of the North Galactic Pole or the Virgo regions, analysed previously. We identify these tentatively as cooling white dwarfs in the Coma Berenices (Mel 111) open cluster.