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1.
Andrés E. Piatti Juan J. Clariá Jean-Claude Mermilliod María C. Parisi Andrea V. Ahumada 《Monthly notices of the Royal Astronomical Society》2007,377(4):1737-1746
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 − M V = 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. 相似文献
2.
M. Tosi L. Pulone G. Marconi & A. Bragaglia 《Monthly notices of the Royal Astronomical Society》1998,299(3):834-844
We present CCD BVI photometry of the old open cluster Berkeley 21, one of the most distant clusters in the Galactic anticentre direction, and possibly the lowest metallicity object in the open clusters sample. Its position and metal abundance make it very important for the study of the Galactic disc. Using the synthetic colour–magnitude diagram method, we estimate values for the distance modulus ( m − M )0 = 13.4–13.6, reddening E ( B − V ) = 0.74–0.78 (with possible differential absorption), and age = 2.2–2.5 Gyr. 相似文献
3.
D. G. Turner †‡§ D. Forbes † D. English ‡ P. J. T. Leonard J. N. Scrimger A. W. Wehlau R. L. Phelps † L. N. Berdnikov § E. N. Pastukhova 《Monthly notices of the Royal Astronomical Society》2008,388(1):444-456
Photoelectric, photographic and CCD UBV photometry, spectroscopic observations and star counts are presented for the open cluster Berkeley 58 to examine a possible association with the 4.37 d Cepheid CG Cas. The cluster is difficult to separate from the early-type stars belonging to the Perseus spiral arm, in which it is located, but has reasonably well-defined parameters: an evolutionary age of ∼108 yr, a mean reddening of E ( B − V ) (B0) = 0.70 ± 0.03 s.e. and a distance of 3.03 ± 0.17 kpc ( V 0 − M V = 12.40 ± 0.12 s.d.). CG Cas is a likely cluster coronal member on the basis of radial velocity, and its period increase of +0.170 ± 0.014 s yr−1 and large light amplitude describe a Cepheid in the third crossing of the instability strip lying slightly blueward of strip centre. Its inferred reddening and luminosity are E ( B − V ) = 0.64 ± 0.02 s.e. and 〈 M V 〉=−3.06 ± 0.12 . A possible K supergiant may also be a cluster member. 相似文献
4.
Andrés E. Piatti Juan J. Clariá Andrea V. Ahumada 《Monthly notices of the Royal Astronomical Society》2009,397(2):1073-1083
We present CCD photometry in the Johnson U , B and V and Kron–Cousins I passbands for the open cluster NGC 2587. The sample consists of 4406 stars reaching down to V ∼ 21.0 . We developed a new method to clean statistically the colour–magnitude diagrams. NGC 2587 appears to be a sparse, relatively bright open cluster, with a few tens of members projected on to a populous star field. The comparatively bright F7/8 II type star HD 70927, located close to the cluster centre, seems not to be a member. Our analysis suggests that NGC 2587 is slightly younger than the Hyades and probably of solar metallicity. A cluster radius of roughly 8 arcmin was estimated from the radial stellar density profile. From 18 probable cluster members with measured proper motions, we derive the following mean values for NGC 2587: μα =−4.3 ± 3.6 mas yr−1 and μδ =−2.5 ± 3.4 mas yr−1 . Adopting the theoretical metal content Z = 0.02 , which provides the best global fit, we derive a cluster age of 500+60 −50 . Simultaneously, colour excesses E ( B − V ) = 0.10 and E ( V − I ) = 0.15 and an apparent distance modulus of V − MV = 12.50 are obtained. The interstellar extinction in the cluster direction is found to follow the normal law. NGC 2587 is located at a distance of (2.70 ± 0.70) kpc from the Sun and ∼9.8 kpc from the Galactic centre. 相似文献
5.
Zhen-Yu Wu Xu Zhou Jun Ma Cui-Hua Du 《Monthly notices of the Royal Astronomical Society》2009,399(4):2146-2164
We present and analyse the kinematics and orbits for a sample of 488 open clusters (OCs) in the Galaxy. The velocity ellipsoid for our present sample is derived as (σ U , σ V , σ W ) = (28.7, 15.8, 11.0) km s−1 which represents a young thin-disc population. We also confirm that the velocity dispersions increase with the age of a cluster subsample. The orbits of OCs are calculated with three Galactic gravitational potential models. The errors of orbital parameters are also calculated considering the intrinsic variation of the orbital parameters and the effects of observational uncertainties. The observational uncertainties dominate the errors of derived orbital parameters. The vertical motions of clusters calculated using different Galactic disc models are rather different. The observed radial metallicity gradient of clusters is derived with a slope of b =−0.070 ± 0.011 dex kpc−1 . The radial metallicity gradient of clusters based on their apogalactic distances is also derived with a slope of b =−0.082 ± 0.014 dex kpc−1 . The distribution of derived orbital eccentricities for OCs is very similar to that derived for the field population of dwarfs and giants in the thin disc. 相似文献
6.
Giovanni Carraro Brian Chaboyer James Perencevich 《Monthly notices of the Royal Astronomical Society》2006,365(3):867-873
The first charge-coupled device UBV ( RI )C photometric study in the area of the doubtful open cluster NGC 2129 is presented. Photometry of a field offset 15 arcmin northwards is also provided, to probe the Galactic disc population towards the cluster. Using star counts, proper motions from the UCAC2 catalogue, colour–magnitude and colour–colour diagrams, we demonstrate that NGC 2129 is a young open cluster. The cluster radius is 2.5 arcmin, and across this region we find evidence of significant differential reddening, although the reddening law seems to be normal towards its direction. Updated estimates of the cluster fundamental parameters are provided. The mean reddening is found to be E ( B − V ) = 0.80 ± 0.08 and the distance modulus is ( m − M )0 = 11.70 ± 0.30 . Hence, NGC 2129 is located at 2.2 ± 0.2 kpc from the Sun inside the Local spiral arm. The age derived from 37 photometrically selected members is estimated to be approximately 10 Myr. These stars are used to provide new estimates of the cluster absolute proper-motion components. 相似文献
7.
M. Gieles 《Monthly notices of the Royal Astronomical Society》2009,394(4):2113-2126
Several recent studies have shown that the star cluster initial mass function (CIMF) can be well approximated by a power law, with indications for a steepening or truncation at high masses. This contribution considers the evolution of such a mass function due to cluster disruption, with emphasis on the part of the mass function that is observable in the first ∼1 Gyr. A Schechter type function is used for the CIMF, with a power-law index of −2 at low masses and an exponential truncation at M * . Cluster disruption due to the tidal field of the host galaxy and encounters with giant molecular clouds flattens the low-mass end of the mass function, but there is always a part of the 'evolved Schechter function' that can be approximated by a power law with index −2. The mass range for which this holds depends on age, τ, and shifts to higher masses roughly as τ0.6 . Mean cluster masses derived from luminosity-limited samples increase with age very similarly due to the evolutionary fading of clusters. Empirical mass functions are, therefore, approximately power laws with index −2, or slightly steeper, at all ages. The results are illustrated by an application to the star cluster population of the interacting galaxy M51, which can be well described by a model with M * = (1.9 ± 0.5) × 105 M⊙ and a short (mass-dependent) disruption time destroying M * clusters in roughly a Gyr. 相似文献
8.
Aaron J. Grocholski Ata Sarajedini 《Monthly notices of the Royal Astronomical Society》2003,345(3):1015-1029
We present combined optical/near-infrared photometry ( BVIK ) for six open clusters – M35, M37, NGC 1817, NGC 2477, NGC 2420 and M67. The open clusters span an age range from 150 Myr to 4 Gyr and have metal abundances from [Fe/H]=−0.27 to +0.09 dex. We have utilized these data to test the robustness of theoretical main sequences constructed by several groups as denoted by the following designations – Padova, Baraffe, Y2 , Geneva and Siess. The comparisons of the models with the observations have been performed in the [ MV , ( B − V )0 ], [ MV , ( V − I )0 ] and [ MV , ( V − K )0 ] colour–magnitude diagrams as well as the distance-independent [( V − K )0 , ( B − V )0 ] and [( V − K )0 , ( V − I )0 ] two-colour diagrams. We conclude that none of the theoretical models reproduces the observational data in a consistent manner over the magnitude and colour range of the unevolved main sequence. In particular, there are significant zero-point and shape differences between the models and the observations. We speculate that the crux of the problem lies in the precise mismatch between theoretical and observational colour–temperature relations. These results underscore the importance of pursuing the study of stellar structure and stellar modelling with even greater intensity. 相似文献
9.
A. K. Dambis 《Monthly notices of the Royal Astronomical Society》2009,396(1):553-569
We use accurate absolute proper motions and Two-Micron All-Sky Survey Ks -band apparent magnitudes for 364 Galactic RR Lyrae variables to determine the kinematical parameters of the Galactic RR Lyrae population and constrain the zero-point of the Ks -band period–luminosity relation for these stars via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be [ U 0 (Halo), V 0 (Halo), W 0 (Halo)]= (−12 ± 10, −217 ± 9, −6 ± 6) km s−1 and [ U 0 (Disc), V 0 (Disc), W 0 (Disc)]= (−15 ± 7, −44 ± 7, −25 ± 5) km s−1 , respectively, and the corresponding components of the velocity-dispersion ellipsoids, [σ VR (Halo), σ V θ (Halo), σ W (Halo)]= (167 ± 9, 86 ± 6, 78 ± 5) km s−1 and [σ VR (Disc), σ V θ (Disc), σ W (Disc)]= (55 ± 7, 44 ± 6, 30 ± 4) km s−1 , respectively. The fraction of thick-disc stars is estimated at 0.25 ± 0.03 . The corrected infrared period–luminosity relation is , implying a Large Magellanic Cloud (LMC) distance modulus of 18.27 ± 0.08 and a solar Galactocentric distance of 7.58 ± 0.40 kpc . Our results suggest no or slightly prograde rotation for the population of halo RR Lyraes in the Milky Way. 相似文献
10.
S. Britzen A. Witzel T. P. Krichbaum T. Beckert R. M. Campbell C. Schalinski J. Campbell 《Monthly notices of the Royal Astronomical Society》2005,362(3):966-974
We present deep CCD BVI photometry of the distant, old open cluster Berkeley 22, covering from the red giant branch (RGB) to about six magnitudes below the main-sequence (MS) turn-off. Using the synthetic colour–magnitude diagram method with three different types of stellar evolutionary tracks, we estimate values and theoretical uncertainties of the distance modulus ( m − M )0 , reddening E ( B − V ), age τ and approximate metallicity. The best fit to the data is obtained for 13.8 ≤ ( m − M )0 ≤ 14.1, 0.64 ≤ E ( B − V ) ≤ 0.65, 2.0 ≤τ≤ 2.5 Gyr (depending on the amount of overshooting from convective regions adopted in the stellar models) and solar metallicity. 相似文献
11.
J. R. D. Lépine Wilton S. Dias Yu. Mishurov 《Monthly notices of the Royal Astronomical Society》2008,386(4):2081-2090
A new method to measure the epicycle frequency κ in the Galactic disc is presented. We make use of the large data base on open clusters completed by our group to derive the observed velocity vector (amplitude and direction) of the clusters in the Galactic plane. In the epicycle approximation, this velocity is equal to the circular velocity given by the rotation curve, plus a residual or perturbation velocity, of which the direction rotates as a function of time with the frequency κ. Due to the non-random direction of the perturbation velocity at the birth time of the clusters, a plot of the present-day direction angle of this velocity as a function of the age of the clusters reveals systematic trends from which the epicycle frequency can be obtained. Our analysis considers that the Galactic potential is mainly axis-symmetric, or in other words, that the effect of the spiral arms on the Galactic orbits is small; in this sense, our results do not depend on any specific model of the spiral structure. The values of κ that we obtain provide constraints on the rotation velocity of the disc; in particular, V 0 is found to be 230 ± 15 km s−1 even if the short scale ( R 0 = 7.5 kpc) of the Galaxy is adopted. The measured κ at the solar radius is 43 ± 5 km s−1 kpc −1 . The distribution of initial velocities of open clusters is discussed. 相似文献
12.
NGC 663 is a young, moderately rich open cluster, known to contain one of the largest fractions of Be stars among all galactic clusters. In this work we present CCD u v by β photometry for stars in its central area. We have used these data to obtain the main cluster physical parameters. We find that the reddening is highly variable, with values ranging from E ( b − y ) = 0.639 ± 0.032 in the central part to E ( b − y ) = 0.555 ± 0.038 in the south-east. The distance modulus is found to be 11.6 ± 0.1 mag (2.1 kpc) and the age log t = 7.4 ± 0.1 yr (25+7 −5 Myr) . The age obtained is consistent with the interpretation of the Be phenomenon as an evolutionary effect. 相似文献
13.
Annapurni Subramaniam Bhuwan Chandra Bhatt 《Monthly notices of the Royal Astronomical Society》2007,377(2):829-834
We present a UBV CCD photometric study of four open clusters, NGC 7245, King 9, IC 166 and King 13, located between l = 90° and 135°. All are embedded in a rich Galactic field. NGC 7245 and King 9 are close together in the sky and have similar reddenings. The distances and ages are: NGC 7245, 3.8 ± 0.35 kpc and 400 Myr; King 9 (the most distant cluster in this quadrant), 7.9 ± 1.1 kpc and 3.0 Gyr. King 13 is 3.1 ± 0.3 kpc distant and 300 Myr old. King 9 and IC 166 (4.8 ± 0.5 kpc distant and 1 Gyr old) may be metal-poor clusters ( Z = 0.008) , as estimated from isochrone fitting. The average value of the distance of young clusters from the Galactic plane in the above longitude range and beyond 2 kpc (−47 ± 16 pc, for 64 clusters) indicates that the young disc bends towards the southern latitudes. 相似文献
14.
Antonis E. Georgakakis Duncan A. Forbes Jean P. Brodie 《Monthly notices of the Royal Astronomical Society》2001,324(4):785-796
We study the globular cluster (GC) system of the dust-lane elliptical galaxy NGC 6702, using B -, V - and I -band imaging observations carried out at the Keck telescope. This galaxy has a spectroscopic age of ≈2 Gyr suggesting recent star formation. We find strong evidence for a bimodal GC colour distribution, with the blue peak having a colour similar to that of the Galactic halo GCs. Assuming that the blue GCs are indeed old and metal-poor, we estimate an age of 2–5 Gyr and supersolar metallicity for the red GC subpopulation. Despite the large uncertainties, this is in reasonable agreement with the spectroscopic galaxy age. Additionally, we estimate a specific frequency of S N =2.3±1.1 for NGC 6702. We predict that passive evolution of NGC 6702 will further increase its specific frequency to S N ≈2.7 within 10 Gyr, in closer agreement to that of typical present-day ellipticals. We also discuss evidence that the merger/accretion event that took place a few Gyr ago involved a high gas fraction. 相似文献
15.
Samantha J. Penny Christopher J. Conselice 《Monthly notices of the Royal Astronomical Society》2008,383(1):247-257
We present the result of a photometric and Keck low-resolution imaging spectrometer (LRIS) spectroscopic study of dwarf galaxies in the core of the Perseus Cluster, down to a magnitude of M B =−12.5 . Spectra were obtained for 23 dwarf-galaxy candidates, from which we measure radial velocities and stellar population characteristics from absorption line indices. From radial velocities obtained using these spectra, we confirm 12 systems as cluster members, with the remaining 11 as non-members. Using these newly confirmed cluster members, we are able to extend the confirmed colour–magnitude relation for the Perseus Cluster down to M B =−12.5 . We confirm an increase in the scatter about the colour–magnitude relationship below M B =−15.5 , but reject the hypothesis that very red dwarfs are cluster members. We measure the faint-end slope of the luminosity function between M B =−18 and −12.5, finding α=−1.26 ± 0.06 , which is similar to that of the field. This implies that an overabundance of dwarf galaxies does not exist in the core of the Perseus Cluster. By comparing metal and Balmer absorption line indices with α-enhanced single stellar population models, we derive ages and metallicities for these newly confirmed cluster members. We find two distinct dwarf elliptical populations: an old, metal-poor population with ages ∼8 Gyr and metallicities [Fe/H] < −0.33 , and a young, metal-rich population with ages <5 Gyr and metallicities [Fe/H] > −0.33 . Dwarf galaxies in the Perseus Cluster are therefore not a simple homogeneous population, but rather exhibit a range in age and metallicity. 相似文献
16.
We report the identification, from a photometric, astrometric and spectroscopic study, of a massive white dwarf member of the nearby, approximately solar metallicity, Coma Berenices open star cluster (Melotte 111). We find the optical to near-infrared energy distribution of WD 1216+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 eff = 15 739+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 ≳ 0.036 M⊙ (spatially unresolved) and M ≳ 0.034 M⊙ (spatially resolved and a ≲ 2500 au ). Based on the predictions of CO core, thick H layer evolutionary models we determine the mass and cooling time of WD 1216+260 to be M WD = 0.90 ± 0.04 M⊙ and τcool = 363+46 −41 Myr , respectively. For an adopted cluster age of τ= 500 ± 100 Myr we infer the mass of its progenitor star to be M init = 4.77+5.37 −0.97 M⊙ . We briefly discuss this result in the context of the form of the stellar initial mass–final mass relation. 相似文献
17.
M. Bellazzini N. Gennari F. R. Ferraro 《Monthly notices of the Royal Astronomical Society》2005,360(1):185-193
We present V and I photometry of a 9.4 × 9.4 arcmin2 field centred on the dwarf spheroidal galaxy Leo II. The tip of the red giant branch (TRGB) is identified at I TRGB = 17.83 ± 0.03 and adopting 〈[M/H]〉=−1.53 ± 0.2 from the comparison of RGB stars with Galactic templates, we obtain a distance modulus ( m − M )0 = 21.84 ± 0.13 , corresponding to a distance D = 233 ± 15 kpc . Two significant bumps have been detected in the luminosity function of the RGB. The fainter bump (B1, at V = 21.76 ± 0.05 ) is the RGB bump of the dominant stellar population while the actual nature of the brightest one (B2, at V = 21.35 ± 0.05 ) cannot be firmly assessed on the basis of the available data; it may be due to the asymptotic giant branch clump of the main population or it may be a secondary RGB bump. The luminosity of the main RGB bump (B1) suggests that the majority of RGB stars in Leo II belong to a population that is ≳4 Gyr younger than the classical Galactic globular clusters. The stars belonging to the He-burning red clump are shown to be significantly more centrally concentrated than RR Lyrae and blue horizontal branch stars, probing the existence of an age/metallicity radial gradient in this remote dwarf spheroidal. 相似文献
18.
P. D. Dobbie R. Napiwotzki M. R. Burleigh M. A. Barstow D. D. Boyce S. L. Casewell R. F. Jameson I. Hubeny G. Fontaine 《Monthly notices of the Royal Astronomical Society》2006,369(1):383-389
We report the spectroscopic confirmation of four further white dwarf members of Praesepe. This brings the total number of confirmed white dwarf members to 11, making this the second largest collection of these objects in an open cluster identified to date. This number is consistent with the high-mass end of the initial mass function of Praesepe being Salpeter in form. Furthermore, it suggests that the bulk of Praesepe white dwarfs did not gain a substantial recoil kick velocity from possible asymmetries in their loss of mass during the asymptotic giant branch phase of evolution. By comparing our estimates of the effective temperatures and the surface gravities of WD0833+194, WD0840+190, WD0840+205 and WD0843+184 to modern theoretical evolutionary tracks, we have derived their masses to be in the range 0.72–0.76 M⊙ and their cooling ages ∼300 Myr. For an assumed cluster age of 625 ± 50 Myr, the inferred progenitor masses are between 3.3 and 3.5 M⊙ . Examining these new data in the context of the initial mass–final mass relation, we find that it can be adequately represented by a linear function ( a 0 = 0.289 ± 0.051, a 1 = 0.133 ± 0.015) over the initial mass range 2.7–6 M⊙ . Assuming an extrapolation of this relation to larger initial masses is valid and adopting a maximum white dwarf mass of 1.3 M⊙ , our results support a minimum mass for core-collapse supernovae progenitors in the range ∼6.8–8.6 M⊙ . 相似文献
19.
We present deep wide-field (16.4×16.4 arcmin2 ) Washington CT 1 CCD surface photometry of the giant elliptical galaxy NGC 4472, the brightest member of the Virgo cluster. Our data cover a wider and deeper field than any previous CCD photometry. A single King model does not give a good fit to the surface brightness profiles of NGC 4472, but they can be fitted approximately using two King models: with the separate models representing the inner and outer regions . Surface brightness profiles for the outer region can also be fitted approximately by a de Vaucouleurs law. There is clearly a negative colour gradient within 3 arcmin of NGC 4472, in the sense that the colour gets bluer with increasing radius. The slope of the colour gradient for this region is derived to be Δ μ ( C − T 1 )=−0.08 mag arcsec−2 for Δ log r =1, which corresponds to a metallicity gradient of Δ[Fe/H]=−0.2 dex. However, the surface colour becomes gradually redder with increasing radius beyond 3 arcmin. A comparison of the structural parameters of NGC 4472 in C and T 1 images has shown that there is little difference in the shapes of ellipses observed using isochromes or isophotes. In addition, photometric and structural parameters of NGC 4472 have been determined. 相似文献
20.
Ferdinando Patat Giovanni Carraro 《Monthly notices of the Royal Astronomical Society》2001,325(4):1591-1602
We report on the first UBVRI CCD photometry of three poorly known star clusterings in the region of η Carinae: Bochum 9, 10 and 11. We find that they are young, rather poor, loose open clusters.
We argue that Bochum 9 is probably a small and loose open cluster with about 30 probable members having E ( B − V )=0.63±0.08 , located 4.6 kpc far from the Sun, beyond the Carina spiral arm.
Similarly, Bochum 10 is a sparse aggregate with 14 probable members having E ( B − V )=0.47±0.05 and at a distance of 2.7 kpc from the Sun.
Finally, Bochum 11 is a less than 4×106 yr old cluster for which we identify 24 members. It has a reddening E ( B − V )=0.58±0.05 , and lies between Bochum 10 and 9, at 3.5 kpc from the Sun. We propose that in the field of the cluster some stars might be pre-main-sequence candidates. 相似文献
We argue that Bochum 9 is probably a small and loose open cluster with about 30 probable members having E ( B − V )=0.63±0.08 , located 4.6 kpc far from the Sun, beyond the Carina spiral arm.
Similarly, Bochum 10 is a sparse aggregate with 14 probable members having E ( B − V )=0.47±0.05 and at a distance of 2.7 kpc from the Sun.
Finally, Bochum 11 is a less than 4×10