Time-series \emph{VI} CCD photometry of the globular cluster NGC 1261 is employed to study its variable star population. A membership analysis of most variables based on Gaia~DR2 proper motions and colours, was performed prior to the estimation of the mean cluster distance and metallicity. For the member RR Lyrae, their light curves were Fourier decomposed to calculate their individual values of distance, [Fe/H], radius and mass. The $I$-band P-L for RR Lyrae stars was also employed. Our best estimates of the metallicity and distance of this Oo I cluster are [Fe/H]$_{\rm ZW}$=$-1.42 \pm 0.05$ dex and $d=17.2 \pm 0.4$ kpc. No mixture of fundamental and first overtone RR Lyrae stars in the either-or or bimodal region is seen in this cluster, as it seems to be the rule for Oo~I clusters with a red horizontal branch. A multi-approach search in a region of about 10$\times$10 arcmin$^2$ around the cluster revealed no new variable stars within the limitations of our CCD photometry.
We present optical and infrared photometric and spectroscopic studies of two Be stars in the 70--80-Myr-old open cluster NGC 6834. NGC 6834(1) has been reported as a binary from speckle interferometric studies whereas NGC 6834(2) may possibly be a gamma Cas-like variable. Infrared photometry and spectroscopy from the United Kingdom Infrared Telescope (UKIRT), and optical data from various facilities are combined with archival data to understand the nature of these candidates. High signal-to-noise near-IR spectra obtained from UKIRT have enabled us to study the optical depth effects in the hydr…
Type Ia supernovae are heavily used tools in precision cosmology, yet we still are not certain what the progenitor systems are. General plausibility arguments suggest there is potential for identifying double degenerate Type Ia supernova progenitors in intermediate-age open star clusters. We present time-resolved high-resolution spectroscopy of two white dwarfs in the field of the open cluster NGC 6633 that had previously been identified as candidate double degenerates in the cluster. However, three hours of continuous observations of each candidate failed to detect any significant radial velo…
We present the results from 10 nights of observations of the globular cluster NGC 6981 (M72) in the V, R and I Johnson wavebands. We employed the technique of difference image analysis to perform precision differential photometry on the time-series images, which enabled us to carry out a census of the under-studied variable star population of the cluster. We show that 20 suspected variables in the literature are actually non-variable, and we confirm the variable nature of another 29 variables while refining their ephemerides. We also detect 11 new RR Lyrae variables and 3 new SX Phe variables,…
This is the first in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to better understand how the RR Lyrae stars in Oosterhoff-intermediate systems compare to those in Oosterhoff I/II systems. In this paper we present the results of our new time-series BV photometric study of NGC 1466. A total of 62 variables were identified in the cluster, of which 16 are new discoveries. The variables include 30 RRab stars, 11 RRc's, 8 RRd's, 1 candidate RR Lyrae, 2 long-period variables, 1 potential anomalous Cepheid, and 9 varia…
This is the second in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to study how RR Lyrae stars in Oosterhoff-intermediate systems compare to their counterparts in Oosterhoff I/II systems. In this paper, we present the results of our new time-series BV photometeric study of the globular cluster NGC 1786. A total of 65 variable stars were identified in our field of view. These variables include 53 RR Lyraes (27 RRab, 18 RRc, and 8 RRd), 3 classical Cepheids, 1 Type II Cepheid, 1 Anomalous Cepheid, 2 eclipsing binar…
Space photometric time series of the most massive members of the young open cluster NGC 2264 allow us to study their different sources of variability down to the millimagnitude level and permits a search for Slowly Pulsating B (SPB) type pulsation among objects that are only a few million years old. Our goal is to conduct a homogeneous study of young B type stars in the cluster NGC 2264 using photometric time series from space in combination with high-resolution spectroscopy and spectropolarimetry obtained from the ground. The latter will be presented in a separate follow-up article. We perfor…
We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of ~50,000 stars in the Lagoon Nebula \ion{H}{2} region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5 < P < 10 d; the short-period cutoff corresponds to breakup. We observe no obvious bimodality in the period distribution, but w…
A campaign on the open cluster NGC 5617 was organized in order to characterize the pulsations and to better understand the internal structure of its stars. The variability of the cluster members was never studied before. We present the observations taken and an up-to-date analysis of the obtained time series, especially of several SPB candidates we discovered.
A compilation of photometric time-series data of NGC 4147 spanning 58 years, enabled to study the secular behaviour of the pulsation period in the population of RR Lyrae stars in the cluster. The traditional O-C diagram approach was employed. Three stars display a significant period decrease and two a comparable period increase. Nevertheless, the median value of the whole sample is nearly zero, which seems consistent with theoretical expectations. The limitations of empirical determinations of secular period changes in globular clusters to corroborate evolutionary theoretical predictions are d…
We present new time-series CCD photometry, in the B and V bands, for the moderately metal-rich ([Fe/H] ~ -1.3) Galactic globular cluster (GC) M62 (NGC 6266). The present dataset is the largest obtained so far for this cluster, and consists of 168 images per filter, obtained with the Warsaw 1.3m telescope at the Las Campanas Observatory (LCO) and the 1.3m telescope of the Cerro Tololo Inter-American Observatory (CTIO), in two separate runs over the time span of three months. The procedure adopted to detect the variable stars was the optimal image subtraction method (ISIS v2.2), as implemented b…
Pulsations in pre-main sequence stars have been discovered several times within the last years. But nearly all of these pulsators are of delta Scuti-type. gamma Doradus-type pulsation in young stars has been predicted by theory, but lack observational evidence. We present the investigation of variability caused by rotation and (gammaDoradus-type) pulsation in two pre-main sequence members of the young open cluster NGC2264 using high-precision time series photometry from the CoRoT satellite and dedicated high-resolution spectroscopy. Time series photometry of NGC2264VAS20 and NGC 2264VAS87 was …
We present a new time-series VI CCD photometry of the globular cluster NGC 6397, from which we obtained and analysed the light curves of 35 variables carefully identified in the cluster field. We assessed the membership of the variables with an astrometric analysis based on \emph{Gaia} DR2 data. The cluster colour-magnitude diagram was differentially dereddened and cleaned of non members, which allowed us to fit isochrones for [Fe/H]$ = -2.0$ dex in the range 13.0--13.5 Gyr, for a mean reddening $E(B-V)=0.19$, and a distance of 2.5 kpc. This distance was confirmed using the period-luminosity r…
We have combined resolved stellar photometry from Hubble Space Telescope (\emph{HST}), \emph{Spitzer}, and \emph{Gaia} to identify red supergiant (RSG) candidates in NGC~6946, based on their colors, proper motions, visual morphologies, and spectral energy distributions. We start with a large sample of 17,865 RSG candidates based solely on \emph{HST} near-infrared photometry. We then chose a small sample of 385 of these candidates with Spitzer matches for more detailed study. Using evolutionary models and isochrones, we isolate a space where RSGs would be found in our photometry catalogs. We th…
New Insights from Revisiting the Rotation Period of the Strongly Magnetic O Star, NGC 1624-2
University of Delaware（特拉华大学）；Queen’s University（女王大学）；Royal Military College of Canada（加拿大皇家军事学院）；National Research Council of Canada（加拿大国家研究委员会）；Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心（CAB），西班牙科学研究中心-国家航空航天技术研究所）；Central Michigan University（中密歇根大学）；California Lutheran University（加州路德大学）；Paris Observatory, PSL University, CNRS, Sorbonne University, Université Paris Cité（巴黎天文台，PSL大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）
Variability is a signature property of cool young stars, particularly for those surrounded by disks. Traditional single-band time series display complex features associated with accretion, disk structure, and accompanying stellar activity, but these processes are challenging to model. To make progress in connecting observed time domain properties with the underlying physics of young stars and their disks, we have embarked on an unprecedented multiwavelength monitoring campaign: the Coordinated Synoptic Investigation of NGC 2264 ("CSI 2264"). Beginning in December 2011, CSI 2264 has acquired 30…
NGC 1624-2 is the most strongly magnetized O-type star known. Previous spectroscopic observations of this object in the ultraviolet provided evidence that it hosts a large and dense circumstellar magnetosphere. Follow-up observations obtained with the \textit{Hubble Space Telescope} not only confirm that previous inference, but also suggest that NGC 1624-2's magnetosphere has a complex structure. Furthermore, an expanded spectropolarimetric time series shows a potential departure from a dipolar magnetic field geometry, which could mean that the strongest field detected at the surface of an O-t…
The NASA space telescope Kepler has provided unprecedented time-series observations which have revolutionised the field of asteroseismology, i.e. the use of stellar oscillations to probe the interior of stars. The Kepler-data include observations of stars in open clusters, which are particularly interesting for asteroseismology. One of the clusters observed with Kepler is NGC 6811, which is the target of the present paper. However, apart from high-precision time-series observations, sounding the interiors of stars in open clusters by means of asteroseismology also requires accurate and precise…
NGC 2808 is a unique globular cluster with not only a bimodal-horizontal branch (HB) but also with gaps on the blue horizontal branch. Adequate interpretation of the nature of the detected peculiarities in "bimodal" and "gap" clusters is of paramount importance for understanding the nature of the second parameter phenomenon and scenarios for the formation of the Galaxy. Although RR Lyrae variables are HB stars that can provide powerful constraints to models on the origin of bimodal HBs, unfortunately, until recently, only one RR Lyrae variable was known in this cluster. Here we present the fir…
We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possibl…
We report the results of CCD $V$, $r$ and $I$ time-series photometry of the globular cluster NGC 5053. New times of maximum light are given for the eight known RR Lyrae stars in the field of our images and their periods are revised. Their $V$ light curves were Fourier decomposed to estimate their physical parameters. A discussion on the accuracy of the Fourier-based iron abundances, temperatures, masses and radii is given. New periods are found for the 5 known SX Phe stars and a critical discussion of their secular period changes is offered. The mean iron abundance for the RR Lyrae stars is fo…
To constrain models of high-mass star formation, the Herschel/HOBYS KP aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC6334, one of the best-studied HOBYS molecular cloud complexes. We used Herschel PACS and SPIRE 70-500mu images of the NGC6334 complex complemented with (sub)millimeter and mid-infrared data. We built a complete procedure to extract ~0.1 pc dense cores with the getsources software, which simultaneously measures their far-infrared to millimeter f…
Context. Stellar physical properties of star clusters are poorly known. Aims. Our goals are to perform a spectrophotometric study of the B star population in open clusters to derive accurate stellar parameters, search for the presence of circumstellar envelopes, and discuss the characteristics of these stars. Methods. The BCD spectrophotometric system is a powerful tool to obtain fundamental parameters and infer the main properties of open clusters: distance modulus, color excess, and age. We inspected the Balmer discontinuity to seek circumstellar disks and identify Be-star candidates. High r…
Time-series photometry of the CoRoT field SRa01 was carried out with the Berlin Exoplanet Search Telescope II (BEST II) in 2008/2009. A total of 1,161 variable stars were detected, of which 241 were previously known and 920 are newly found. Several new, variable young stellar objects have been discovered. The study of the spatial distribution of eclipsing binaries revealed the higher relative frequency of Algols toward the center of the young open cluster NGC 2264. In general Algol frequency obeys an isotropic distribution of their angular momentum vectors, except inside the cluster, where a s…
We report the discovery of two new variable stars in the metal-poor globular cluster NGC 288, found by means of time-series CCD photometry. We classified the new variables as SX Phoenicis due to their characteristic fundamental mode periods (1.02 +- 0.01 and 0.69 +- 0.01 hours), and refine the period estimates for other six known variables. SX Phe stars are known to follow a well-defined Period-Luminosity (P-L) relation and, thus, can be used for determining distances; they are more numerous than RR Lyraes in NGC~288. We obtain the P-L relation for the fundamental mode M_V = (-2.59 +- 0.18) lo…
The Galactic globular clusters (GGCs) located in the inner regions of the Milky Way suffer from high extinction that makes their observation challenging. The VVV survey provides a way to explore these GGCs in the near-infrared where extinction effects are highly diminished. We conduct a search for variable stars in several inner GGCs, taking advantage of the unique multi-epoch, wide-field, near-infrared photometry provided by the VVV survey. We are especially interested in detecting classical pulsators that will help us constrain the physical parameters of these GGCs. In this paper, the second…
We identify 228 periodic variables in the region of young open cluster NGC 281 using time series photometry carried out from 1 m class ARIES telescopes, Nainital. The cluster membership of these identified variables is determined on the basis colour-magnitude, two colour diagrams and kinematic data. Eighty one variable stars are found to be members of the cluster NGC 281. Of 81 variables, 30 and 51 are probable main-sequence and pre-main-sequence members, respectively. Present study classifies main-sequence variable stars into different variability types according to their periods of variabili…
We present time series photometry of 57 variable stars in the cluster region NGC 7380. The association of these variable stars to the cluster NGC 7380 has been established on the basis of two colour diagrams and colour-magnitude diagrams. Seventeen stars are found to be main-sequence variables, which are mainly B type stars and are classified as slowly pulsating B stars, $β$ Cep or $δ$ Scuti stars. Some of them may belong to new class variables as discussed by Mowlavi et al. (2013) and Lata et al. (2014). Present sample also contains 14 pre-main-sequence stars, whose ages and masses are found …
We present HST/STIS time-series spectroscopy of the central star of the "Cat's Eye" planetary nebula NGC 6543. Intensive monitoring of the UV lines over a 5.8 hour period reveals well defined details of large-scale structure in the fast wind, which are exploited to provide new constraints on the rotation rate of the central star. We derive characteristics of the line profile variability that support a physical origin due to co-rotating interaction regions (CIRs) that are rooted at the stellar surface. The recurrence time of the observed spectral signatures of the CIRs is used to estimate the r…
We present results of time series photometry to search for variable stars in the field of metal-poor globular cluster NGC 4590 (M68). Periods have been revised for 40 known variables and no significant changes were found. A considerable change in Blazhko effect for V25 has been detected. Among nine newly discovered variable candidates, 5 stars are of RRc Bailey type variables while 4 stars are unclassified. The variable stars V10, V21, V50 and V51 are found to be cluster members based on the radial velocity data taken from literature.
We present an expanded kinematic study of the young cluster NGC 2264 based upon optical radial velocities measured using multi-fiber echelle spectroscopy at the 6.5 meter MMT and Magellan telescopes. We report radial velocities for 695 stars, of which approximately 407 stars are confirmed or very likely members. Our results more than double the number of members with radial velocities from F{\H u}r{é}sz et al., resulting in a much better defined kinematic relationship between the stellar population and the associated molecular gas. In particular, we find that there is a significant subset of s…
We re-examine the properties of the star cluster population in the circumnuclear starburst ring in the face-on spiral galaxy NGC 7742, whose young cluster mass function has been reported to exhibit significant deviations from the canonical power law. We base our reassessment on the clusters' luminosities (an observational quantity) rather than their masses (a derived quantity), and confirm conclusively that the galaxy's starburst-ring clusters---and particularly the youngest subsample, $\log(t \mbox{ yr}^{-1}) \le 7.2$---show evidence of a turnover in the cluster luminosity function well above…
The {\emph{Kepler}} space telescope has provided exquisite data to perform asteroseismic analysis on evolved star ensembles. Studying star clusters offers significant insight into stellar evolution and structure, due to having a large number of stars with essentially the same age, distance, and chemical composition. This study analysed eight solar-like oscillating evolved stars that are members of the open cluster NGC 6811 and modelled them for the first time. The fundamental stellar parameters are obtained from the interior model using observational asteroseismic and non-asteroseismic constra…
We report an analysis of new $V$ and $I$ CCD time-series photometry of the globular cluster NGC 6934. Through the Fourier decomposition of the RR Lyrae light curves, the mean values of [Fe/H] and the distance of the cluster were estimated, we found; [Fe/H]$_{UVES}$=-1.48$\pm$0.14 and $d$=16.03$\pm$0.42 kpc, and [Fe/H]$_{UVES}$=-1.43$\pm$0.11 and $d$=15.91$\pm$0.39 kpc, from the calibrations of RRab and RRc stars respectively. Independent distance estimations from SX Phe and SR stars are also discussed. Individual absolute magnitudes, radii and masses are also reported for RR Lyrae stars. We fo…
In this paper we present time series photometry of 104 variable stars in the cluster region NGC 1893. The association of the present variable candidates to the cluster NGC 1893 has been determined by using $(U-B)/(B-V)$ and $(J-H)/(H-K)$ two colour diagrams, and $V/(V-I)$ colour magnitude diagram. Forty five stars are found to be main-sequence variables and these could be B-type variable stars associated with the cluster. We classified these objects as $β$ Cep, slowly pulsating B stars and new class variables as discussed by Mowlavi et al. (2013). These variable candidates show $\sim$0.005 to …
A few star clusters in the Magellanic Clouds exhibit composite structures in the red-clump region of their colour-magnitude diagrams. The most striking case is NGC419 in the SMC, where the red clump is composed of a main blob as well as a distinct secondary feature. This structure is demonstrated to be real and corresponds to the simultaneous presence of stars which passed through electron degeneracy after central-hydrogen exhaustion and those that did not. This rare occurrence in a single cluster allows us to set stringent constraints on its age and on the efficiency of convective-core oversh…
We present an asteroseismological study on the two high-gravity pulsating PG1159 (GW Vir or DOV) stars, PG 2131+066 and PG 1707+427, and on the pulsating [WCE] star NGC 1501. We compute adiabatic $g$-mode pulsation periods on PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 Msun. These models take into account the complete evolution of progenitor stars, through the thermally pulsing AGB phase, and born-again episode. We constrain the stellar mass of PG 2131+066, PG 1707+427 and NGC 1501 by comparing the observed period spacing with the asymptotic period spacing and wi…
We report the results of a time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2126. In about one square degree field covering the cluster, a total number of 21 variable candidates are detected during this survey, of which 16 are newly found. The periods, classifications and spectral types of 14 newly discovered variables are discussed, which consist of six eclipsing binaries systems, three pulsating variable stars, three long period variables, one RS CVn star, and one W UMa or $δ$ Scuti star. In addition, there are two variable candidates, the properties …
We present results of a search for variable stars in a region of the globular cluster NGC 4147 based on photometric observations with 4k x 4k CCD imager mounted at the axial port of the recently installed 3.6 m Devasthal optical telescope at Aryabhatta Research Institute of Observational Sciences, Nainital, India. We performed time series photometry of NGC 4147 in V and R bands, and identified 42 periodic variables in the region of NGC 4147, 28 of which have been detected for the first time. Seventeen variable stars are located within the half light radius $\lesssim$ 0.48 arcmin, of which 10 s…
This paper presents the Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B, V and R filters by using Nanshan 1m telescope of Xinjiang Astronomical Observatory. 19 variable stars and 3 variable candidates were detected in a 45 {\times} 48.75 field around the cluster. 12 of the variable stars are newly-discovered variable objects. The physical properties, classifications, and membership of the 22 objects are studied through their light curves, their positions on the color-magnitude diagram, and with the archival data f…
Two previously unknown variable stars in the crowded central region of the globular cluster NGC 6981 are presented. The observations were made using the Electron Multiplying CCD (EMCCD) camera at the Danish 1.54m Telescope at La Silla, Chile.The two variables were not previously detected by conventional CCD imaging because of their proximity to a bright star. This discovery demonstrates that EMCCDs are a powerful tool for performing high-precision time-series photometry in crowded fields and near bright stars, especially when combined with difference image analysis (DIA).
Continuing our series of papers on the 3-D structure and accurate distances of Planetary Nebulae (PNe), we present here the results obtained for the planetary nebula NGC\,40. Using data from different sources and wavelengths, we construct 3-D photoionization models and derive the physical quantitities of the ionizing source and nebular gas. The procedure, discussed in detail in the previous papers, consists of the use of 3-D photoionization codes constrained by observational data to derive the three-dimensional nebular structure, physical and chemical characteristics and ionizing star paramete…
We wish to measure the cool star rotation period distribution for the Pleiades-age rich open cluster NGC 2516 and use it to determine whether cluster-to-cluster variations exist in otherwise identical open clusters. We obtained 42 d-long time-series CCD photometry of NGC 2516 using the Yale 1 m telescope at CTIO and performed a number of related analyses, including PSF-based time-series photometry. Our data are complemented with additional information from several photometric datasets, literature radial velocities, and Gaia DR2 astrometry. All available data are used to construct an integrated…
New time-series VI CCD photometry of the globular cluster NGC 6362 is studied with the aim of estimating the reddening, mean metallicity and distance of the cluster from its population of RR Lyrae stars. The Fourier decomposition of carefully selected single-mode RR Lyrae light curves, and the use of well-established semi-empirical calibrations and revised zero points, lead to the values of [Fe/H]UVES =1:066 +// 0:126 and -1:08 +/- 0:16 and the distance 7:93 +/- 0:32 and 8:02 +/- 0:15 kpc from the RRab and RRc stars respectively. The distribution of RR Lyrae stars in the horizontal branch show…
(Abridged) Following on from a recently completed radial-velocity survey of the old (7 Gyr) open cluster NGC 188 in which we study in detail the solar-type hard binaries and blue stragglers of the cluster, here we investigate the dynamical evolution of NGC 188 through a sophisticated N-body model. We employ the observed binary properties of the young (150 Myr) open cluster M35, where possible, to guide our choices for parameters of the initial binary population. At 7 Gyr the main-sequence solar-type hard-binary population in the model matches that of NGC 188 in both binary frequency and distri…
In this paper, we present the analysis of time-series observations from 2013 and 2014 of five metal rich ([Fe/H] $>$ -1) globular clusters: NGC~6388, NGC~6441, NGC~6528, NGC~6638, and NGC~6652. The data have been used to perform a census of the variable stars in the central parts of these clusters. The observations were made with the electron multiplying CCD (EMCCD) camera at the Danish 1.54m Telescope at La Silla, Chile, and they were analysed using difference image analysis (DIA) to obtain high-precision light curves of the variable stars. It was possible to identify and classify all of the …
Recently, Kundu et al (2019) reported that the globular cluster NGC 5024 (M53) possesses five extra-tidal RR Lyrae. In fact, four of them were instead known members of a nearby globular cluster NGC 5053. The status of the remaining extra-tidal RR Lyrae is controversial depending on the adopted tidal radius of NGC 5024. We have also searched for additional extra-tidal RR Lyrae within an area of $\sim8$~deg$^2$ covering both globular clusters. This includes other known RR Lyrae within the search area, as well as stars that fall within the expected range of magnitudes and colors for RR Lyrae (and…
We present a study of variable stars in globular cluster NGC 6401. The cluster is only $5.3\degr$ away from the Galactic centre and suffers from strong differential reddening. The photometric precision afforded us by difference image analysis resulted in improved sensitivity to variability in formerly inaccessible interior regions of the cluster. We find 23 RRab and 11 RRc stars within one cluster radius (2.4$\arcmin$), for which we provide coordinates, finder-charts and time-series photometry. Through Fourier decomposition of the RR Lyrae star light curves we derive a mean metallicity of [Fe/…
We analyzed the high-resolution spectra of a large sample of AGB and RGB stars in the Galactic globular clusters (GCs) NGC 104, NGC 6121, and NGC 6809 obtained with FLAMES/GIRAFFE at ESO/VLT, and determined their Na abundances. This is the first time that the AGB stars in NGC 6809 are targeted. Moreover, we reanalyzed with the same method the data archive for NGC 6752. To investigate the dependence of AGB Na abundance dispersion on GC parameters, we compared the AGB [Na/H] distributions we obtained (including NGC 2808 presented in the first paper of this series) with literature data for four o…
In this paper we analyse the evolutionary status and properties of the old open cluster NGC 2355, located in the Galactic anticentre direction, as a part of the long term programme BOCCE. NGC 2355 was observed with LBC@LBT using the Bessel $B$, $V$, and $I_c$ filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram (CMD) method, as done in other papers of this series. Additional spectroscopic observations with FIES@NOT of three giant stars were used to determine the chemical properties of the cluster. Our analysis shows that NGC 2355 has metallicity sligh…
We have investigated the variable stars in the field surrounding NGC 2355 based on the time-series photometric observation data. More than 3000 CCD frames were obtained in the V band spread over 13 nights with the Nanshan One-meter Wide-field Telescope. We have detected 88 variable stars, containing 72 new variable stars and 16 known variable stars. By analyzing these light curves, we classified the variable stars as follows: 26 eclipsing binaries, 52 pulsating stars, 4 rotating variables, and 6 unclear type variable stars for which their periods are much longer than the time baseline chosen. …
Previous studies on the stellar content of the two nearby dwarf galaxies NGC147 and NGC185 reveal a rich population of late-type giants in both systems, including a large number of carbon-rich objects. These stars are known to show pronounced photometric variability, which can be used for a more detailed characterisation of these highly evolved stars. Owing to their well-studied parameters, these Local Group members are ideal candidates for comparative studies. Trough photometric monitoring, we attempt to provide a catalogue of long-period variables (LPVs), including Mira variables, semi-regul…
We obtained FLAMES GIRAFFE+UVES spectra for both first and second-generation red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them to derive abundances of 21 atomic species for a sample of 92 stars. The surveyed elements include proton-capture (O, Na, Mg, Al, Si), alpha-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be clustered into two discrete groups along the Na-O anti-corr…
We present VI-band photometry for stars in the metal-rich globular cluster NGC 6496. Our time-series data were cadenced to search for long period variables (LPVs) over a span of nearly two years, and our variability search yielded the discovery of thirteen new variable stars, of which six are LPVs, two are suspected LPVs, and five are short period eclipsing binaries. An additional star was found in the ASAS database, and we clarify its type and period. We argue that all of the eclipsing binaries are field stars, while 5-6 of the LPVs are members of NGC 6496. We compare the period-luminosity di…
We present a revised distance to the nearby galaxy NGC6822 using a new multi-band fit to both previously published and new optical, near- and mid-infrared data for Cepheid variables. The new data presented in this study include multi-epoch observations obtained in 3.6\um and 4.5\um with the \emph{Spitzer Space Telescope} taken for the Carnegie Hubble Program. We also present new observations in J, H and \kswith FourStar on the Magellan Baade telescope at Las Campanas Observatory. We determine mean magnitudes and present new period-luminosity relations in V, I, J, H, \ks, IRAC 3.6\um and 4.5\um…
We present VLT/FORS2 time-series spectroscopy of the Wolf-Rayet star #41 in the Sculptor group galaxy NGC 300. We confirm a physical association with NGC 300 X-1, since radial velocity variations of the HeII 4686 line indicate an orbital period of 32.3 +/- 0.2 hr which agrees at the 2 sigma level with the X-ray period from Carpano et al. We measure a radial velocity semi-amplitude of 267 +/- 8 km/s, from which a mass function of 2.6 +/- 0.3 Msun is obtained. A revised spectroscopic mass for the WN-type companion of 26+7-5 Msun yields a black hole mass of 20 +/- 4 Msun for a preferred inclinati…
Extended main-sequence turnoffs apparent in most young and intermediate-age clusters (younger than ~2 Gyr) are known features caused by fast rotating early-type (earlier than F-type) stars. Late-type stars are not fast rotators because their initial angular momenta have been quickly dispersed due to magnetic braking. However, the mass limit below which stars have been magnetically braked has not been well constrained by observation. In this paper, we present an analysis of the eMSTO of NGC 6819, an open cluster of an intermediate-age (~2.5 Gyr), believed to be comparable to the lifetime of sta…
Using the MeerKAT radio telescope, a series of observations have been conducted to time the known pulsars and search for new pulsars in the globular cluster NGC 6440. As a result, two pulsars have been discovered, NGC 6440G and NGC 6440H, one of which is isolated and the other a non-eclipsing (at frequencies above 962 MHz) "Black Widow", with a very low mass companion (M$_{\rm c}$ > 0.006 M$_{\odot}$). It joins the other binary pulsars discovered so far in this cluster which all have low companion masses (M$_{\rm c}$ < 0.30 M$_{\odot}$). We present the results of long-term timing solutions obt…
