Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNew Cepheid variables in the young open clusters Berkeley 51 and Berkeley 55
143
0
0.0
(
0
)
Authors
M. E. Lohr
Ask ChatGPT about the research
No Arabic abstract
As part of a wider investigation of evolved massive stars in Galactic open clusters, we have spectroscopically identified three candidate classical Cepheids in the little-studied clusters Berkeley 51, Berkeley 55 and NGC 6603. Using new multi-epoch photometry, we confirm that Be 51 #162 and Be 55 #107 are bona fide Cepheids, with pulsation periods of 9.83+/-0.01 d and 5.850+/-0.005 d respectively, while NGC 6603 star W2249 does not show significant photometric variability. Using the period-luminosity relationship for Cepheid variables, we determine a distance to Be 51 of 5.3(+1.0,-0.8) kpc and an age of 44(+9,-8) Myr, placing it in a sparsely-attested region of the Perseus arm. For Be 55, we find a distance of 2.2+/-0.3 kpc and age of 63(+12,-11) Myr, locating the cluster in the Local arm. Taken together with our recent discovery of a long-period Cepheid in the starburst cluster VdBH222, these represent an important increase in the number of young, massive Cepheids known in Galactic open clusters. We also consider new Gaia (data release 2) parallaxes and proper motions for members of Be 51 and Be 55; the uncertainties on the parallaxes do not allow us to refine our distance estimates to these clusters, but the well-constrained proper motion measurements furnish further confirmation of cluster membership. However, future final Gaia parallaxes for such objects should provide valuable independent distance measurements, improving the calibration of the period-luminosity relationship, with implications for the distance ladder out to cosmological scales.
rate research
Read More
Classical Cepheids in open clusters play an important role in benchmarking stellar evolution models, anchoring the cosmic distance scale, and invariably securing the Hubble constant. NGC 6649, NGC 6664 and Berkeley 55 are three pertinent clusters that host classical Cepheids and red (super)giants, and an analysis was consequently initiated to assess newly acquired spectra ($approx$50), archival photometry, and $Gaia$ DR2 data. Importantly, for the first time chemical abundances are determined for the evolved members of NGC 6649 and NGC 6664. We find that they are slightly metal-poor relative to the mean Galactic gradient, and an overabundance of Ba is observed. Those clusters likely belong to the thin disc, and the latter finding supports DOrazi et al. (2009) $s$-enhanced scenario. NGC 6664 and Berkeley 55 exhibit radial velocities consistent with Galactic rotation, while NGC 6649 displays a peculiar velocity. The resulting age estimates for the clusters ($approx$70 Ma) imply masses for the (super)giant demographic of $approx$6 M$_{sun}$. Lastly, the observed yellow-to-red (super)giant ratio is lower than expected, and the overall differences relative to models reflect outstanding theoretical uncertainties.
We present a $UBVI$ photometric study of the open clusters Berkeley 24 (Be 24) and Czernik 27 (Cz 27). The radii of the clusters are determined as 2farcm7 and 2farcm3 for Be 24 and Cz 27, respectively. We use the Gaia Data Release 2 (GDR2) catalogue to estimate the mean proper motions for the clusters. We found the mean proper motion of Be 24 as $0.35pm0.06$ mas yr$^{-1}$ and $1.20pm0.08$ mas yr$^{-1}$ in right ascension and declination for Be 24 and $-0.52pm0.05$ mas yr$^{-1}$ and $-1.30pm0.05$ mas yr$^{-1}$ for Cz 27. We used probable cluster members selected from proper motion data for the estimation of fundamental parameters. We infer reddenings $E(B-V)$ = $0.45pm0.05$ mag and $0.15pm0.05$ mag for the two clusters. Analysis of extinction curves towards the two clusters show that both have normal interstellar extinction laws in the optical as well as in the near-IR band. From the ultraviolet excess measurement, we derive metallicities of [Fe/H]= $-0.025pm0.01$ dex and $-0.042pm0.01$ dex for the clusters Be 24 and Cz 27, respectively. The distances, as determined from main sequence fitting, are $4.4pm0.5$ kpc and $5.6pm0.2$ kpc. The comparison of observed CMDs with $Z=0.01$ isochrones, leads to an age of $2.0pm0.2$ Gyr and $0.6pm0.1$ Gyr for Be 24 and Cz 27, respectively. In addition to this, we have also studied the mass function and dynamical state of these two clusters for the first time using probable cluster members. The mass function is derived after including the corrections for data incompleteness and field star contamination. Our analysis shows that both clusters are now dynamically relaxed
CCD BVI photometry of the faint open clusters Berkeley~73, Berkeley~75 and Berkeley~25 are presented. The two latter are previously unstudied clusters to our knowledge. While Berkeley~73 is found to be of intermediate-age (about 1.5 Gyr old), Berkeley~75 and Berkeley~25 are two old clusters, with ages larger than 3.0 Gyr. We provide also estimates of the clusters size. Very interestingly, all these clusters turn out to lie far away from the Galactic Center, at $R_{GC} geq$ 16 kpc, and quite high onto the Galactic plane, at $|Z_{odot}| geq 1.5$ kpc. They are therefore important targets to probe the properties of the structure of the Galaxy in this direction, where the Canis Major over-density has been recently discovered to be located.
We present the analysis of the morphological shape of Berkeley 17, the oldest known open cluster (~10 Gyr), using a probabilistic star counting of Pan-STARRS point sources, and confirm its core-tail shape, plus an antitail, previously detected with the 2MASS data. The stellar population, as diagnosed by the color-magnitude diagram and theoretical isochrones, shows many massive members in the cluster core, whereas there is a paucity of such members in both tails. This manifests mass segregation in this aged star cluster with the low-mass members being stripped away from the system. It has been claimed that Berkeley 17 is associated with an excessive number of blue straggler candidates. Comparison of nearby reference fields indicates that about half of these may be field contamination.
Berkeley 59 is a nearby ($sim$1 kpc) young cluster associated with the Sh2-171 H{sc ii} region. We present deep optical observations of the central $sim$2.5$times$2.5 pc$^2$ area of the cluster, obtained with the 3.58-m Telescopio Nazionale Galileo. The $V$/($V$-$I$) color-magnitude diagram manifests a clear pre-main-sequence (PMS) population down to $sim$ 0.2 M$_odot$. Using the near-infrared and optical colors of the low-mass PMS members we derive a global extinction of A$_V$= 4 mag and a mean age of $sim$ 1.8 Myr, respectively, for the cluster. We constructed the initial mass function and found that its global slopes in the mass ranges of 0.2 - 28 M$_odot$ and 0.2 - 1.5 M$_odot$ are -1.33 and -1.23, respectively, in good agreement with the Salpeter value in the solar neighborhood. We looked for the radial variation of the mass function and found that the slope is flatter in the inner region than in the outer region, indicating mass segregation. The dynamical status of the cluster suggests that the mass segregation is likely primordial. The age distribution of the PMS sources reveals that the younger sources appear to concentrate close to the inner region compared to the outer region of the cluster, a phenomenon possibly linked to the time evolution of star-forming clouds is discussed. Within the observed area, we derive a total mass of $sim$ 10$^3$ M$_odot$ for the cluster. Comparing the properties of Berkeley 59 with other young clusters, we suggest it resembles more to the Trapezium cluster.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
