scholarly journals Characterizing low-contrast Galactic open clusters with Gaia Data Release 2

2020 ◽  
Vol 493 (3) ◽  
pp. 3473-3489 ◽  
Author(s):  
M S Angelo ◽  
J F C Santos ◽  
W J B Corradi
Keyword(s):  
Three Dimensional ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Galactocentric Distance ◽  
Low Contrast ◽  
Crossing Time ◽  
Data Release ◽  
Solar Metallicity ◽  
Formation Conditions ◽  
Considerable Range

ABSTRACT In this study, we characterized 16 objects previously classified as faint or low-contrast Galactic open clusters (OCs). We employed parameters associated with the dynamical evolution of the OCs: the core (rc), tidal (rt) and half-mass (rhm) radii, age and crossing time (tcr). Relations among these parameters were exploited to draw some evolutionary connections. We also included 11 OCs with previous characterizations to provide wider coverage of the parameter space. The investigated sample spans a considerable range in age, log (t yr−1) ∼7.0–9.7, and Galactocentric distance, RG ∼ 6–11 kpc). Most of these OCs present solar metallicity. We employed Gaia Data Release 2 astrometry and photometry, and we selected member stars through a decontamination algorithm that explores the three-dimensional astrometric space (μα, μδ, ϖ) to assign membership likelihoods. Previous studies of most of these objects were based mostly on photometric information. All investigated OCs were proved to be real stellar concentrations. The relations among their parameters indicate a general disruption scenario in which OCs tend to be more concentrated as they evolve. Internal interactions sucessively drive OCs to develop more dynamically relaxed structures and make them less subject to mass loss due to tidal effects. Tidal radius tends to increase with RG in accordance with the strength of the Galactic tidal field. Besides, the correlation between rc and the dynamical ratio τdyn = age/tcr suggests two distinct evolutionary sequences, which may be a consequence of different initial formation conditions.

scholarly journals Characterizing dynamical stages of open clusters located in the Sagittarius spiral arm

2019 ◽  
Vol 488 (2) ◽  
pp. 1635-1651 ◽  
Author(s):  
M S Angelo ◽  
A E Piatti ◽  
W S Dias ◽  
F F S Maia
Keyword(s):  
Structural Parameters ◽  
Three Dimensional ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Mass Star ◽  
Proper Motions ◽  
Concentration Parameter ◽  
Low Mass ◽  
Gaia Dr2 ◽  
Spiral Arm

Abstract The study of dynamical properties of Galactic open clusters (OCs) is a fundamental prerequisite for the comprehension of their dissolution processes. In this work, we characterized 12 OCs, namely: Collinder 258, NGC 6756, Czernik 37, NGC 5381, Ruprecht 111, Ruprecht 102, NGC 6249, Basel 5, Ruprecht 97, Trumpler 25, ESO 129−SC32, and BH 150, projected against dense stellar fields. In order to do that, we employed Washington CT1 photometry and Gaia DR2 astrometry, combined with a decontamination algorithm applied to the three-dimensional astrometric space of proper motions and parallaxes. From the derived membership likelihoods, we built decontaminated colour–magnitude diagrams, while structural parameters were obtained from King profiles fitting. Our analysis revealed that they are relatively young OCs (log(t  yr−1) ∼7.3–8.6), placed along the Sagittarius spiral arm, and at different internal dynamical stages. We found that the half-light radius to Jacobi radius ratio, the concentration parameter and the age to relaxation time ratio describe satisfactorily their different stages of dynamical evolution. Those relative more dynamically evolved OCs have apparently experienced more important low-mass star loss.

Compact groups of galaxies (CGs) from the SDSS Data Release 6

Open Physics ◽  
2008 ◽  
Vol 6 (2) ◽  
Author(s):  
Xin-Fa Deng ◽  
Ji-Zhou He ◽  
Xin-sheng Ma ◽  
Peng Jiang ◽  
Xiao-Xun Tang
Keyword(s):  
Cluster Analysis ◽  
Velocity Dispersion ◽  
Three Dimensional ◽  
Compact Groups ◽  
Groups Of Galaxies ◽  
Main Galaxy ◽  
Crossing Time ◽  
Data Release ◽  
Galaxy Sample ◽  
Virial Mass

AbstractFrom the volume-limited MAIN galaxy sample of the SDSS Data Release 6 (SDSS6), we have identified 1298 compact groups of galaxies (CGs) at the neighbourhood radius of R = 1.2 Mpc by three-dimensional cluster analysis. In order to compile the CG catalog, we also estimated velocity dispersion, virial radius, virial mass and crossing time of CGs. In addition, our results show that properties of galaxies may not correlate with merging frequencies.

scholarly journals Investigating dynamical properties of evolved Galactic open clusters

2019 ◽  
Vol 624 ◽  
pp. A8 ◽  
Author(s):  
M. S. Angelo ◽  
J. F. C. Santos ◽  
W. J. B. Corradi ◽  
F. F. S. Maia
Keyword(s):  
Open Cluster ◽  
Three Dimensional ◽  
Dynamical Evolution ◽  
Long Term Evolution ◽  
Open Clusters ◽  
Evolutionary Stage ◽  
Proper Motions ◽  
Stellar Content ◽  
Term Evolution

Context. The stellar content of Galactic open clusters is gradually depleted during their evolution as a result of internal relaxation and external interactions. The final residues of the long-term evolution of open clusters are called open cluster remnants. These are sparsely populated structures that can barely be distinguished from the field. Aims. We aimed to characterise and compare the dynamical states of a set of 16 objects catalogued as remnants or remnant candidates. We employed parameters that are intimately associated with the dynamical evolution: age, limiting radius, stellar mass, and velocity dispersion. The sample also includes 7 objects that are catalogued as dynamically evolved open clusters for comparison purposes. Methods. We used photometric data from the 2MASS catalogue, proper motions and parallaxes from the Gaia DR2 catalogue, and a decontamination algorithm that was applied to the three-dimensional astrometric space of proper motions and parallaxes (μα, μδ, ϖ) for stars in the objects’ areas. The luminosity and mass functions and total masses for most open cluster remnants are derived here for the first time. Our analysis used predictions of N-body simulations to estimate the initial number of stars of the remnants from their dissolution timescales. Results. The investigated open cluster remnants present masses (M) and velocity dispersions (σv) within well-defined ranges: M between ∼10−40 M⊙ and σv between ∼1−7 km s−1. Some objects in the remnant sample have a limiting radius Rlim ≲ 2 pc, which means that they are more compact than the investigated open clusters; other remnants have Rlim between ∼2−7 pc, which is comparable to the open clusters. We suggest that cluster NGC 2180 (previously classified as an open cluster) is entering a remnant evolutionary stage. In general, our clusters show signals of depletion of low-mass stars. This confirms their dynamically evolved states. Conclusions. We conclude that the open cluster remnants we studied are in fact remnants of initially very populous open clusters (N0 ∼ 103−104 stars). The outcome of the long-term evolution is to bring the final residues of the open clusters to dynamical states that are similar to each other, thus masking out the memory of the initial formation conditions of star clusters.

scholarly journals Photometric study of the young open clusters IC 1442, King 21, and Trumpler 7

2020 ◽  
Vol 495 (2) ◽  
pp. 2496-2508 ◽  
Author(s):  
Jayanand Maurya ◽  
Y C Joshi ◽  
A S Gour
Keyword(s):  
Relaxation Time ◽  
Outer Region ◽  
Mass Function ◽  
Open Clusters ◽  
Photometric Study ◽  
Proper Motions ◽  
Dynamical Study ◽  
Data Release ◽  
Solar Metallicity ◽  
Mass Segregation

ABSTRACT We carried out the UBVRcIc photometric study of three poorly studied young open clusters IC 1442, King 21, and Trumpler 7 (Tr 7). We obtained 263, 244, and 128 member stars using Gaia Data Release 2 proper motions and parallaxes in IC 1442, King 21, and Tr 7, respectively. The reddening, E(B − V), was derived to be 0.54 ± 0.04, 0.76 ± 0.06, and 0.38 ± 0.04 mag for these clusters. The comparison of observed colour–magnitude diagrams with solar metallicity isochrones yields log(age) = 7.40 ± 0.30, 7.70 ± 0.20, and 7.85 ± 0.25 yr and corresponding distances of 2847 ± 238, 2622 ± 156, and 1561 ± 74 pc for IC 1442, King 21, and Tr 7, respectively. The estimated mass function (MF) slopes are found to be −1.94 ± 0.18, −1.54 ± 0.32, and −2.31 ± 0.29 for IC 1442, King 21, and Tr 7, respectively. The study of MF slopes done separately in the inner and the outer regions of these clusters gives a steeper slope in the outer region, which suggests spatial variation in slope and mass segregation in the clusters. We found evidence of mass segregation after the dynamical study in these clusters. The obtained relaxation time, TE, is 74, 26, and 34 Myr for the clusters IC 1442, King 21, and Tr 7, respectively. The mass segregation in IC 1442 may be caused by early dynamical relaxation. The estimated TE is well below the ages of King 21 and Tr 7, which indicates that these clusters are dynamically relaxed.

scholarly journals Characterizing dynamical states of Galactic open clusters with Gaia DR2

2020 ◽  
Vol 500 (4) ◽  
pp. 4338-4353
Author(s):  
M S Angelo ◽  
W J B Corradi ◽  
J F C Santos ◽  
F F S Maia ◽  
F A Ferreira
Keyword(s):  
Dynamical Evolution ◽  
Open Clusters ◽  
The Other ◽  
Analysis Method ◽  
Galactocentric Distance ◽  
Tidal Disruption ◽  
Gravitational Fields ◽  
Dynamical Properties ◽  
Astrometric Data ◽  
Gaia Dr2

ABSTRACT In this work, we investigate the dynamical properties of 38 Galactic open clusters: 34 of them are located at low Galactic latitudes (|b| < 10°) and are projected against dense stellar fields; the other four comparison objects present clearer contrasts with the field population. We determine structural and time-related parameters that are associated with the clusters’ dynamical evolution: core (rc), tidal (rt), and half-mass (rhm) radii, ages (t), and crossing times (tcr). We have also incorporated results for 27 previously studied clusters, creating a sample of 65, spanning the age and Galactocentric distance (RG) ranges $7.0 \lt \textrm {log}\, t \lt 9.7$ and 6 < RG (kpc) < 13. We employ a uniform analysis method which incorporates photometric and astrometric data from the Gaia DR2 catalogue. Member stars are identified by employing a decontamination algorithm which operates on the 3D astrometric space of parallax and proper motion and attributes membership likelihoods for stars in the cluster region. Our results show that internal relaxation causes rc to correlate negatively with the dynamical ratio τdyn = t/tcr. This implies that dynamically older systems tend to be more centrally concentrated. The more concentrated ones tend to present smaller rhm/rt ratios, which means that they are less subject to tidal disruption. The analysis of coeval groups at compatible RG suggests that the inner structure of clusters is reasonably insensitive to variations in the external tidal field. Additionally, our results confirm, on average, an increase in rt for regions with less-intense Galactic gravitational fields.

scholarly journals Photometric analysis of newly discovered open clusters SAI 24 and SAI 94 based on PPMXL catalogue

2019 ◽  
pp. 45-53
Author(s):  
W.H. Elsanhoury ◽  
Magdy Amin
Keyword(s):  
Galactic Plane ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Cluster Center ◽  
Crossing Time ◽  
Magnitude Diagram ◽  
The Masses ◽  
Mass Functions ◽  
Projected Distance

In our present work, we studied the photometric characteristics (core radius, limiting radius, reddening... etc.) as well as their dynamical state of the two newly discovered open clusters, SAI 24 and SAI 94. We investigated their photometric properties in the J, H, and Ks bands with the PPMXL catalogue. A method of separating open cluster stars from those belonging to the stellar background has been employed. The results of our calculations indicate that the numbers of probable members in SAI 24 and SAI 94 are 202 and 199, respectively. We have estimated the cluster center for SAI 24, i.e. ?2000 = 02h 59m 26 .s36 and ?2000 = 60? 33' 02.''50 and for SAI 94 is ?2000 = 08h 10m 16 .s36, ?2000 = ?46? 17' 07.''91. The core radii rcore for SAI 24 and SAI 94 are found to be (1.92 ? 0.38) arcmin and (1.22 ? 0.10) arcmin, respectively and in the same manner the limiting radii rlim are about (2.45 ? 0.64) and (3.07 ? 0.57) arcmin. From the color-magnitude diagram, in view of the approximate logarithmic ages for SAI 24 and SAI 94 of 7.20 ? 0.20 and 9.10 ? 0.05, their distances are estimated to be (930 ? 30) pc and (3515 ? 60) pc, respectively. Also, we have calculated their projected distances (X? and Y?) to the Galactic plane and the projected distance Z? from the Galactic plane. The luminosity and mass functions of SAI 24 and SAI 94 clusters were outlined; accordingly, the masses were calculated to be (285 ? 17) M? and (317 ? 18) M?, respectively. Finally, we concluded that these two clusters are dynamically relaxed according to our estimation of their dynamical evolution parameter ? as a function of their crossing time Tcross. The evaporation time ?ev as a function of their relaxation time Trelax is about 6.18 Myr and 25.38 Myr for SAI 24 and SAI 94, respectively.

Exploring Coronal Structures with SOHO

2000 ◽  
Vol 179 ◽  
pp. 403-406
Author(s):  
M. Karovska ◽  
B. Wood ◽  
J. Chen ◽  
J. Cook ◽  
R. Howard
Keyword(s):  
Solar Corona ◽  
Image Enhancement ◽  
Coronal Mass Ejections ◽  
Dynamical Evolution ◽  
Small Scale ◽  
Low Contrast ◽  
Contrast Structures ◽  
Scale Structures ◽  
Small Scale Structures ◽  
Coronal Structures

AbstractWe applied advanced image enhancement techniques to explore in detail the characteristics of the small-scale structures and/or the low contrast structures in several Coronal Mass Ejections (CMEs) observed by SOHO. We highlight here the results from our studies of the morphology and dynamical evolution of CME structures in the solar corona using two instruments on board SOHO: LASCO and EIT.

High-speed brightfield 3-D imaging and 3-D image analysis of thick and overlapped cell clusters in cytological preparations

1994 ◽  
Vol 52 ◽  
pp. 218-219
Author(s):  
Robert W. Mackin
Keyword(s):  
Image Analysis ◽  
High Speed ◽  
Three Dimensional ◽  
Image Data ◽  
Ccd Camera ◽  
Objective Lens ◽  
Array Processor ◽  
Vaginal Smears ◽  
Low Contrast ◽  
Computer Controlled

This paper presents two advances towards the automated three-dimensional (3-D) analysis of thick and heavily-overlapped regions in cytological preparations such as cervical/vaginal smears. First, a high speed 3-D brightfield microscope has been developed, allowing the acquisition of image data at speeds approaching 30 optical slices per second. Second, algorithms have been developed to detect and segment nuclei in spite of the extremely high image variability and low contrast typical of such regions. The analysis of such regions is inherently a 3-D problem that cannot be solved reliably with conventional 2-D imaging and image analysis methods.High-Speed 3-D imaging of the specimen is accomplished by moving the specimen axially relative to the objective lens of a standard microscope (Zeiss) at a speed of 30 steps per second, where the stepsize is adjustable from 0.2 - 5μm. The specimen is mounted on a computer-controlled, piezoelectric microstage (Burleigh PZS-100, 68/μm displacement). At each step, an optical slice is acquired using a CCD camera (SONY XC-11/71 IP, Dalsa CA-D1-0256, and CA-D2-0512 have been used) connected to a 4-node array processor system based on the Intel i860 chip.

scholarly journals Formation rate of LB-1-like systems through dynamical interactions

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Ataru Tanikawa ◽  
Tomoya Kinugawa ◽  
Jun Kumamoto ◽  
Michiko S Fujii
Keyword(s):  
Open Cluster ◽  
Formation Rate ◽  
Open Clusters ◽  
Type Star ◽  
Dynamical Mechanism ◽  
Milky Way Galaxy ◽  
Triple Systems ◽  
Stellar Collisions ◽  
Solar Metallicity ◽  
Helium Star

Abstract We estimate formation rates of LB-1-like systems through dynamical interactions in the framework of the theory of stellar evolution before the discovery of the LB-1 system. The LB-1 system contains a ∼70 ${M_{\odot}}$ black hole (BH), a so-called pair instability (PI) gap BH, and a B-type star with solar metallicity, and has nearly zero eccentricity. The most efficient formation mechanism is as follows. In an open cluster, a naked helium star (with ∼20 ${M_{\odot}}$) collides with a heavy main sequence star (with ∼50 ${M_{\odot}}$) which has a B-type companion. The collision results in a binary consisting of the collision product and the B-type star with a high eccentricity. The binary can be circularized through the dynamical tide with radiative damping of the collision product envelope. Finally, the collision product collapses to a PI-gap BH, avoiding pulsational pair instability and pair instability supernovae because its He core is as massive as the pre-colliding naked He star. We find that the number of LB-1-like systems in the Milky Way galaxy is ∼0.01(ρoc/104 ${M_{\odot}}$ pc−3), where ρoc is the initial mass densities of open clusters. If we take into account LB-1-like systems with O-type companion stars, the number increases to ∼0.03(ρoc/104 ${M_{\odot}}$ pc−3). This mechanism can form LB-1-like systems at least ten times more efficiently than the other mechanisms: captures of B-type stars by PI-gap BHs, stellar collisions between other types of stars, and stellar mergers in hierarchical triple systems. We conclude that no dynamical mechanism can explain the presence of the LB-1 system.

scholarly journals The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14

2019 ◽  
Vol 626 ◽  
pp. A16 ◽  
Author(s):  
A. Rojas-Arriagada ◽  
M. Zoccali ◽  
M. Schultheis ◽  
A. Recio-Blanco ◽  
G. Zasowski ◽  
...  
Keyword(s):  
Fundamental Parameters ◽  
Elemental Abundances ◽  
Data Release ◽  
Bulge Region ◽  
Solar Metallicity ◽  
Inner Region ◽  
Clean Sample ◽  
Metallicity Distribution ◽  
Single Sequence

Context. The Galactic bulge has a bimodal metallicity distribution function: different kinematic, spatial, and, potentially, age distributions characterize the metal-poor and metal-rich components. Despite this observed dichotomy, which argues for different formation channels for those stars, the distribution of bulge stars in the α-abundance versus metallicity plane has been found so far to be a rather smooth single sequence. Aims. We use data from the fourteenth data release of the APOGEE spectroscopic survey (DR14) to investigate the distribution in the Mg abundance (as tracer of the α-elements)-versus-metallicity plane of a sample of stars selected to be in the inner region of the bulge. Methods. A clean sample has been selected from the DR14 using a set of data- and pipeline-flags to ensure the quality of their fundamental parameters and elemental abundances. An additional selection made use of computed spectro-photometric distances to select a sample of likely bulge stars as those with RGC ≤ 3.5 kpc. We adopt magnesium abundance as an α-abundance proxy for our clean sample as it has been proven to be the most accurate α-element as determined by ASPCAP, the pipeline for data products from APOGEE spectra. Results. From the distribution of our bulge sample in the [Mg/Fe]-versus-[Fe/H] plane, we found that the sequence is bimodal. This bimodality is given by the presence of a low-Mg sequence of stars parallel to the main high-Mg sequence over a range of ∼0.5 dex around solar metallicity. The two sequences merge above [Fe/H] ∼ 0.15 dex into a single sequence whose dispersion in [Mg/Fe] is larger than either of the two sequences visible at lower metallicity. This result is confirmed when we consider stars in our sample that are inside the bulge region according to trustworthy Gaia DR2 distances.

Sign in / Sign up

Export Citation Format

Share Document