Context. The reddening maps of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are constructed using the Cepheid period–luminosity (P–L) relations. Aims. We examine reddening ...distribution across the LMC and SMC through large data sets on classical Cepheids provided by the OGLE Phase IV survey. We also investigate the age and spatio-temporal distributions of Cepheids to understand the recent star formation history in the LMC and SMC. Methods. The V and I band photometric data of 2476 fundamental mode (FU) and 1775 first overtone mode (FO) Cepheids in the LMC, and 2753 FU and 1793 FO Cepheids in the SMC were analysed for their P–L relations. We converted the period of FO Cepheids to the corresponding period of FU Cepheids before combining the two modes of Cepheids. Both galaxies were divided into small segments and combined FU and FO P–L diagrams were drawn in two bands for each segment. The reddening analysis was performed on 133 segments covering a total area of about 154.6 deg2 in the LMC and 136 segments covering a total area of about 31.3 deg2 in the SMC. By comparison with well-calibrated P–L relations of these two galaxies, we determined reddening E(V − I) in each segment and equivalent reddening E(B − V) assuming the normal extinction law. The period–age relations were used to derive the age of the Cepheids. Results. Reddening maps were constructed using reddening values in different segments across the LMC and SMC. We find clumpy structures in the reddening distributions of the LMC and SMC. From the reddening map of the LMC, highest reddening of E(V − I) = 0.466 mag is traced in the region centred at α ∼ 85.°13, δ ∼ −69.°34 α ∼ 85 . ° 13 , δ ∼ − 69 . ° 34 $ \alpha \sim 85{{\overset{\circ}{.}}}13,~\delta \sim -69{{\overset{\circ}{.}}}34 $ which is in close vicinity of the star forming HII region 30 Doradus. In the SMC, maximum reddening of E(V − I) = 0.189 mag is detected in the region centred at α ∼ 12.°10, δ ∼ −73.°07 α ∼ 12 . ° 10 , δ ∼ − 73 . ° 07 $ \alpha \sim 12{{\overset{\circ}{.}}}10,~\delta \sim -73{{\overset{\circ}{.}}}07 $ . The mean reddening values in the LMC and SMC are estimated as E(V − I)LMC = 0.113 ± 0.060 mag, E(B − V)LMC = 0.091 ± 0.050 mag, E(V − I)SMC = 0.049 ± 0.070 mag, and E(B − V)SMC = 0.038 ± 0.053 mag. Conclusions. The LMC reddening map displays heterogeneous distribution having small reddening in the central region and higher reddening towards the eastern side of the LMC bar. The SMC has relatively small reddening in its peripheral regions but larger reddening towards the south-west region. In these galaxies, we see evidence of a common enhanced Cepheid population at around 200 Myr ago which appears to have occurred due to a close encounter between the two clouds.
Context. Significant progress has been made in recent years to understand the formation and evolution of our Galaxy, but we still lack a complete understanding of the Galaxy and its structure. Aims. ...Using an almost complete sample of Galactic open star clusters within 1.8 kpc, we aim to understand the general properties of the open cluster system in the Galaxy and probe the Galactic structure. Methods. We first extracted 1241 open clusters within 1.8 kpc of the Sun from the Milky Way Star Clusters (MWSC) catalog. Considering it an almost complete sample of clusters within this distance, we performed a comprehensive statistical analysis of various cluster parameters such as spatial position, age, size, mass, and extinction. Results. We find an average cluster scale height of zh = 60 ± 2 pc for clusters younger than 700 Myr, which increases to 64 ± 2 pc when we include all the clusters. The zh is found to be strongly dependent on RGC and age, and on an average, zh is more than twice as large as in the outer region than in the inner region of the solar circle, except for the youngest population of clusters. The solar offset is found to be 6.2 ± 1.1 pc above the formal Galactic plane. We derive a local mass density of ρ0 = 0.090 ± 0.005 M⊙/ pc3 and estimate a negligibly small amount of dark matter in the solar neighborhood. The reddening in the direction of clusters suggests a strong correlation with their vertical distance from the Galactic plane with a respective slope of dE(B−V) / dz = 0.40 ± 0.04 and 0.42 ± 0.05 mag/kpc below and above the Galactic plane. We observe a linear mass-radius and mass-age relations in the open clusters and derive the slopes of dR/ d(log M) = 2.08 ± 0.10 and d(log M) / d(log T) = −0.36 ± 0.05, respectively. Conclusions. The dependence of the spatial distribution of clusters on their age points to a complex interplay between cluster formation and survivability within the Galaxy. The geometrical characteristics of a significant number of clusters enabled us to understand large-scale spatial properties of the cluster systems within the Galaxy. The structural and physical parameters of clusters allowed us to check mutual correlations between the individual parameters.
Abstract
We present the photometric and spectroscopic analysis of four W UMa binaries J015829.5+260333 (hereinafter as J0158), J030505.1+293443 (hereinafter as J0305), J102211.7+310022 (hereinafter ...as J1022), and KW Psc. The
VR
c
I
c
band photometric observations are carried out with the 1.3 m Devasthal Fast Optical Telescope (DFOT). For low-resolution spectroscopy, we used the 2 m Himalayan Chandra Telescope (HCT) as well as the archival data from the 4 m LAMOST survey. The systems J0158 and J0305 show a period increase rate of 5.26( ± 1.72) × 10
−7
days yr
−1
and 1.78( ± 1.52) × 10
−6
days yr
−1
, respectively. The period of J1022 is found to be decreasing with a rate of 4.22 ( ± 1.67) × 10
−6
days yr
−1
. The period analysis of KW Psc displays no change in its period. The PHOEBE package is used for the light-curve modeling and basic parameters are evaluated with the help of the GAIA parallax. The asymmetry of light curves is explained with the assumption of cool spots at specific positions on one of the components of the system. On the basis of temperatures, mass ratios, fill-out factors, and periods, the system J1022 is identified as a W-subtype system while the others show some mixed properties. To probe the chromospheric activities in these W UMa binaries, their spectra are compared with the known inactive stars’ spectra. The comparison shows emission in
H
α
,
H
β
, and Ca
II
. To understand the evolutionary status of these systems, the components are plotted in mass–radius and mass–luminosity planes with other well characterized binary systems. The secondary components of all the systems are away from ZAMS, which indicates that the secondary is more evolved than the primary component.
ABSTRACT
We present UBVRcIc photometric study of three intermediate age open star clusters NGC 381, NGC 2360, and Berkeley 68 (Be 68). We examine the cluster membership of stars using recently ...released Gaia DR2 proper motions and obtain a total of 116, 332, and 264 member stars in these three clusters. The mean reddening of E(B − V) = 0.36 ± 0.04, 0.08 ± 0.03, and 0.52 ± 0.04 mag is found in the direction of these clusters where we observe an anomalous reddening towards NGC 381. We fitted the solar metallicity isochrones to determine age and distance of the clusters which are found to be log(Age) = 8.65 ± 0.05, 8.95 ± 0.05, and 9.25 ± 0.05 yr with the respective distance of 957 ± 152, 982 ± 132, and 2554 ± 387 pc for the clusters NGC 381, NGC 2360, and Be 68. A two-stage power law in the mass function (MF) slope is observed in the cluster NGC 381, however, we observe only a single MF slope in the clusters NGC 2360 and Be68. To study a possible spatial variation in the slope of MF, we estimate slopes separately in the inner and the outer regions of these clusters and notice a steeper slope in outer region. The dynamic study of these clusters reveals deficiency of low-mass stars in their inner regions suggesting the mass segregation process in all these clusters. The relaxation times of 48.5, 78.9, and 87.6 Myr are obtained for the clusters NGC 381, NGC 2360, and Be 68, respectively, which are well below to their respective ages. This suggests that all the clusters are dynamically relaxed.
We present near-UV transmission spectroscopy of the highly irradiated transiting exoplanet WASP-12b, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. The spectra cover ...three distinct wavelength ranges: NUVA (2539-2580 A), NUVB (2655-2696 A), and NUVC (2770-2811 A). Three independent methods all reveal enhanced transit depths attributable to absorption by resonance lines of metals in the exosphere of WASP-12b. Light curves of total counts in the NUVA and NUVC wavelength ranges show a detection at a 2.5{sigma} level. We detect extra absorption in the Mg II {lambda}{lambda}2800 resonance line cores at the 2.8{sigma} level. The NUVA, NUVB, and NUVC light curves imply effective radii of 2.69 {+-} 0.24 R {sub J}, 2.18 {+-} 0.18 R {sub J}, and 2.66 {+-} 0.22 R {sub J} respectively, suggesting the planet is surrounded by an absorbing cloud which overfills the Roche lobe. We detect enhanced transit depths at the wavelengths of resonance lines of neutral sodium, tin, and manganese, and at singly ionized ytterbium, scandium, manganese, aluminum, vanadium, and magnesium. We also find the statistically expected number of anomalous transit depths at wavelengths not associated with any known resonance line. Our data are limited by photon noise, but taken as a whole the results are strong evidence for an extended absorbing exosphere surrounding the planet. The NUVA data exhibit an early ingress, contrary to model expectations; we speculate this could be due to the presence of a disk of previously stripped material.
Intestinal epithelial stem cells (ISCs) are the focus of recent intense study. Current in vitro models rely on supplementation with the Wnt agonist R-spondin1 to support robust growth, ISC ...self-renewal, and differentiation. Intestinal subepithelial myofibroblasts (ISEMFs) are important supportive cells within the ISC niche. We hypothesized that co-culture with ISEMF enhances the growth of ISCs in vitro and allows for their successful in vivo implantation and engraftment. ISC-containing small intestinal crypts, FACS-sorted single ISCs, and ISEMFs were procured from C57BL/6 mice. Crypts and single ISCs were grown in vitro into enteroids, in the presence or absence of ISEMFs. ISEMFs enhanced the growth of intestinal epithelium in vitro in a proximity-dependent fashion, with co-cultures giving rise to larger enteroids than monocultures. Co-culture of ISCs with supportive ISEMFs relinquished the requirement of exogenous R-spondin1 to sustain long-term growth and differentiation of ISCs. Mono- and co-cultures were implanted subcutaneously in syngeneic mice. Co-culture with ISEMFs proved necessary for successful in vivo engraftment and proliferation of enteroids; implants without ISEMFs did not survive. ISEMF whole transcriptome sequencing and qPCR demonstrated high expression of specific R-spondins, well-described Wnt agonists that supports ISC growth. Specific non-supportive ISEMF populations had reduced expression of R-spondins. The addition of ISEMFs in intestinal epithelial culture therefore recapitulates a critical element of the intestinal stem cell niche and allows for its experimental interrogation and biodesign-driven manipulation.
We report on the discovery of WASP-12b, a new transiting extrasolar planet with R pl = 1.79+0.09 -0.09 RJ and M pl = 1.41+0.10 -0.10 M J. The planet and host star properties were derived from a Monte ...Carlo Markov Chain analysis of the transit photometry and radial velocity data. Furthermore, by comparing the stellar spectrum with theoretical spectra and stellar evolution models, we determined that the host star is a supersolar metallicity (M/H = 0.3+0.05 -0.15), late-F (T eff = 6300+200 -100 K) star which is evolving off the zero-age main sequence. The planet has an equilibrium temperature of T eq = 2516 K caused by its very short period orbit (P = 1.09 days) around the hot, twelfth magnitude host star. WASP-12b has the largest radius of any transiting planet yet detected. It is also the most heavily irradiated and the shortest period planet in the literature.
Abstract
We study variable stars in the field of the open cluster NGC 381 using photometric data observed over 27 nights and identify a total of 57 variable stars, six of which are member stars. The ...variable stars are classified based on their periods, amplitudes, light-curve shapes, and locations in the H-R diagram. We found a rich variety of variable stars in the cluster. We identified a total of 10 eclipsing binaries, of which two are of Algol type while eight are of W UMa type (EW). The estimated ages of these EW binaries are greater than 0.6 Gyr, which is in agreement with the formation time constraint of ≥0.6 Gyr on short-period eclipsing binaries. The physical parameters of the two EW-type binaries are estimated using PHOEBE model-fitting software. The pulsating variable stars include one each from the
δ
Scuti and
γ
Dor variability classes. We determined the pulsation modes of pulsating variables with the help of the FAMIAS package. We obtained 15 rotational variable stars comprising four dwarf stars identified on the basis of their log(
g
) versus log(
T
eff
) diagram. These dwarf stars are found to have generally longer periods than the remaining rotational variables.
We have carried out a comparative statistical study for the displacement of the Sun from the Galactic plane (z⊙) following three different methods. The study has been carried out using a sample of ...537 young open clusters (YOCs) with log (Age) < 8.5, lying within a heliocentric distance of 4 kpc, and 2030 OB stars observed up to a distance of 1200 pc, all of which have distance information. We statistically separated the members of the Gould Belt before investigating the variation in the z⊙ estimation with different upper cut-off limits in the heliocentric distance and distance perpendicular to the Galactic plane. We have found that z⊙ varies in the range ∼13–20 pc from the analysis of YOCs and in the range ∼6–28 pc from the analysis of OB stars. A significant scatter in z⊙, because of different cut-off values, is noticed for the OB stars, although no such deviation is seen for the YOCs. We have also determined scaleheights of 56.9+3.8−3.4 and 61.4+2.7−2.4 pc for the distribution of YOCs and OB stars, respectively.
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 μRA = −0.143 ± 0.008 mas yr−1 and μDec. = −3.395 ± 0.008 mas yr−1. 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 d = 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⊙ is found to be γ = −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 arcmin × 13 arcmin region of the cluster. The V-band photometric data accumulated on 43 nights over a period of more than 3 yr reveals 76 variable stars among which 72 are periodic variables. Among them, 59 are short period (P < 1 d) and 13 are long period (P > 1 d). The variable stars have V magnitudes ranging between 9.1 to 19.4 mag and periods between 41 min and 10.74 d. On the basis of their locations in the H–R diagram, periods, and characteristic light curves, 20 periodic variables belong to the cluster are classified as 2 δ-Scuti, 3 γ-Dor, 2 slowly pulsating B stars, 5 rotational variables, 2 non-pulsating B stars, and 6 as miscellaneous variables.
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