Mass segregation

About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.

Star counts, blue stragglers, and mass segregation in NGC 7492

Abstract: New B, V photometry of the sparse globular cluster NGC 7492 is used to construct the cluster color-magnitude diagram (CMD) down to about three magnitudes below the main-sequence turnoff. Adopting a reddening of E(B-V) = 0.00 mag, the cluster metallicity is confirmed to be [Fe/H] = −1.51. The relative-age technique of VandenBerg et al. (1990, Astron. J., 100) implies that NGC 7492 is approximately 1.7 ± 1.2 Gyr older than NGC 6752. A distance modulus of (m-M) 0 = 17.09 ± 0.20 mag has been derived. The discovery of 27 candidate blue stragglers which are found to be more centrally concentrated than the cluster subgiants of similar brightness is reported

K-band luminosity (mass) segregation in AC 118 at z = 0.31

Abstract: Using new observations of the galaxy cluster AC 118 at intermediate redshift (z = 0.31) in the K s band, we were able to detect the cluster from the center to half the Abell radius (1.5 Mpc, H 0 = 50 km s - 1 Mpc - 1 ) andpossibly to 2.0 Mpc. The analysis of both the spatial distribution of galaxies of various luminosities and of the luminosity function (LF) of galaxies in different cluster locations strongly confirms and extends to larger clustercentric radii the luminosity segregation found in a previous analysis of this cluster restricted to a smaller cluster area: there is an excess of bright galaxies in the cluster core (inside 250 Kpc) or a deficit of dwarfs in the remain part of the cluster. Outside the cluster core and as far as 1.5 or even 2 Mpc, the giant-to-dwarf ratio is constant. Because of the luminosity segregation, the LF of the AC 118 shows a larger number of bright galaxies per unit dwarf in the core than in other cluster locations. All non-core LFs, computed at several cluster locations, are compatible each other. These results hold both including or excluding the galaxies located in an overdensity found in the far South of AC118 and in the second clump in galaxy density at the cluster North-West. Since the near-infrared emission is a good tracer of the stellar mass, we interpret the segregation found as a mass segregation.

Photometric, kinematic, and variability study in the young open cluster NGC 1960

Abstract: We present a comprehensive photometric analysis of a young open cluster NGC 1960 (M36) along with the long-term variability study of this cluster. Based on the kinematic data of Gaia DR2, the membership probabilities of 3871 stars are ascertained in the cluster field among which 262 stars are found to be cluster members. Considering the kinematic and trigonometric measurements of the cluster members, we estimate a mean cluster parallax of 0.86+/-0.05 mas and mean proper motions of mu_RA = -0.143+/-0.008 mas/yr, mu_Dec = -3.395+/-0.008 mas/yr. We obtain basic parameters of the cluster such as E(B-V) = 0.24+/-0.02 mag, log(Age/yr)=7.44+/-0.02, and distance = 1.17+/-0.06 kpc. The mass function slope in the cluster for the stars in the mass range of 0.72-7.32 M_solar is found to be \gamma = -1.26+/-0.19. We find that mass segregation is still taking place in the cluster which is yet to be dynamically relaxed. This work also presents first high-precision variability survey in the central 13'x13' among which 72 are periodic variables. Among them, 59 are short-period (P 1 day). The variable stars have V magnitudes ranging between 9.1 to 19.4 mag and periods between 41 minutes to 10.74 days. On the basis of their locations in the H-R diagram, periods and characteristic light curves, the 20 periodic variables belong to the cluster. We classified them as 2 delta-Scuti, 3 gamma-Dor, 2 slowly pulsating B stars, 5 rotational variables, 2 non-pulsating B stars and 6 as miscellaneous variables.

The Open Cluster NGC 7789. I. Radial Velocities for Giant Stars

Abstract: A total of 597 radial velocity observations for 112 stars in the ~1.6 Gyr 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±0.12 km s–1 and the dispersion is 0.86 km s–1, from 50 constant velocity stars selected as members from this radial velocity study and the 1981 proper motion study of McNamara & Solomon. 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 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 for three other clusters, the data strongly support the conclusion that mass segregation is being detected.

Multiwavelength study of a young open cluster NGC 7419

Abstract: Using new UBVRI Hα CCD photometric observations and the archival infrared and X-ray data, we have carried out a multiwavelength study of a Perseus arm young open star cluster NGC 7419. An age of 22.5 ±3.0 Myr and a distance of 3230 +330 -430 pc are derived for the cluster. Our photometric data indicate a higher value of colour excess ratio E(U - B)/E(B - V) than the normal one. There is an evidence for mass segregation in this dynamically relaxed cluster and in the range 1.4-8.6 M ⊙ , the mass function slope is in agreement with the Salpeter value. Excess emissions in near-infrared and Ha support the existence of a young (≤2 Myr) stellar population of Herbig Ae/Be stars (≥3.0 M ⊙ ) indicating a second episode of star formation in the cluster region. Using XMM-Newton observations, we found several X-ray sources in the cluster region but none of the Herbig Ae/Be stars is detected in X-rays. We compare the distribution of upper limits for Herbig Ae/Be stars with the X-ray distribution functions of the T Tauri and the Herbig Ae/Be stars from previous studies, and found that the X-ray emission level of these Herbig Ae/Be stars is not more than L X ∼ 5.2 x 10 30 erg s -1 , which is not significantly higher than for the T Tauri stars. Therefore, X-ray emission from Herbig Ae/Be stars could be the result of either unresolved companion stars or a process similar to T Tauri stars. We report an extended X-ray emission from the cluster region NGC 7419, with a total X-ray luminosity estimate of ∼1.8 x 10 31 erg s -1 arcmin -2 . If the extended emission is due to unresolved emission from the point sources then we estimate ∼288 T Tauri stars in the cluster region each having X-ray luminosity ∼1.0 x 10 30 erg s -1 . Investigation of dust attenuation and 12 CO emission map of a square degree region around the cluster indicates the presence of a foreground dust cloud which is most likely associated with the local arm star-forming region (Sh2-154). This cloud harbours uniformly distributed pre-main-sequence stars (0.1-2.0 M ⊙ ), with no obvious trend of their distribution with either (H - K) excess or A V . This suggests that the star formation in this cloud depend mostly upon the primordial fragmentation.