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891. C stars in Pegasus, DDO 210 and Tucana
ID:
ivo://CDS.VizieR/J/AJ/120/1801
Title:
C stars in Pegasus, DDO 210 and Tucana
Short Name:
J/AJ/120/1801
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the latest results of our ongoing four-filter photometric survey of C stars in Local Group dwarf irregular galaxies. Observations of the two low-luminosity dwarf irregular galaxies, Pegasus and DDO 210, revealed 40 and three C stars, respectively, assuming that the reddening of Pegasus is negligible. No C stars were identified in Tucana. Our observations permit the estimation of the color-magnitude diagram contamination by foreground M dwarfs thus yielding reliable C/M ratios. Our R and I photometry of the C stars cannot be used to solve the extinction controversy toward Pegasus. The three C stars in DDO 210 are quite bright when compared with C star populations in other dwarf galaxies. A larger, fainter population in that galaxy seems improbable, however. The statistics of C stars currently on hand for dwarf galaxies show a well-defined trend with the absolute magnitude of dwarf galaxies.
892. CTIO and WFPC2 photometry in NGC 6822
ID:
ivo://CDS.VizieR/J/AJ/121/2020
Title:
CTIO and WFPC2 photometry in NGC 6822
Short Name:
J/AJ/121/2020
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the massive star population of NGC 6822 with ground-based UBV photometry covering the whole of the galaxy and HST WFPC2 photometry with filters F255W, F336W, F439W, and F555W of two fields containing very rich and crowded OB associations. The four-band WFPC2 photometry is used to derive Teff and E(B-V). H-R diagrams are constructed for the OB associations included in our fields. These show that 10Myr old populations are present in OB 9 and OB 6, while more recent star formation have occurred in OB 8, OB 13, OB 15, and OB 7. Two particularly interesting H II regions, Hubble V and Hubble X, are included in our fields. The luminous massive stars that power these bright H II regions (H{alpha} luminosity several times that of the Orion nebula), could be resolved even in their dense cores thanks to the HST spatial resolution. Our data reveal very young (a few million years), apparently coeval populations, with several massive star candidates.
893. CTIO/DECam LCs for Galactic bulge variable stars
ID:
ivo://CDS.VizieR/J/ApJ/892/112
Title:
CTIO/DECam LCs for Galactic bulge variable stars
Short Name:
J/ApJ/892/112
Date:
21 Oct 2021
Publisher:
CDS
Description:
With the advent of the Legacy Survey of Space and Time, time-domain astronomy will be faced with an unprecedented volume and rate of data. Real-time processing of variables and transients detected by such large-scale surveys is critical to identifying the more unusual events and allocating scarce follow-up resources efficiently. We develop an algorithm to identify these novel events within a given population of variable sources. We determine the distributions of magnitude changes (dm) over time intervals (dt) for a given passband f, p_f_^(dm|dt)^, and use these distributions to compute the likelihood of a test source being consistent with the population or being an outlier. We demonstrate our algorithm by applying it to the DECam multiband time-series data of more than 2000 variable stars identified by Saha+ (2019, J/ApJ/874/30) in the Galactic Bulge that are largely dominated by long-period variables and pulsating stars. Our algorithm discovers 18 outlier sources in the sample, including a microlensing event, a dwarf nova, and two chromospherically active RS CVn stars, as well as sources in the blue horizontal branch region of the color-magnitude diagram without any known counterparts. We compare the performance of our algorithm for novelty detection with the multivariate Kernel Density Estimator and Isolation Forest on the simulated PLAsTiCC data set. We find that our algorithm yields comparable results despite its simplicity. Our method provides an efficient way for flagging the most unusual events in a real-time alert-broker system.
894. CTIO/DECam photometry of RR Lyrae stars in M5
ID:
ivo://CDS.VizieR/J/AJ/154/85
Title:
CTIO/DECam photometry of RR Lyrae stars in M5
Short Name:
J/AJ/154/85
Date:
21 Oct 2021
Publisher:
CDS
Description:
We characterize the absolute magnitudes and colors of RR Lyrae stars in the globular cluster M5 in the ugriz filter system of the Dark Energy Camera (DECam). We provide empirical period-luminosity (P-L) relationships in all five bands based on 47 RR Lyrae stars of the type ab and 14 stars of the type c. The P-L relationships were found to be better constrained for the fundamental-mode RR Lyrae stars in the riz passbands, with dispersions of 0.03, 0.02 and 0.02mag, respectively. The dispersion of the color at minimum light was found to be small, supporting the use of this parameter as a means to obtain accurate interstellar extinctions along the line of sight up to the distance of the RR Lyrae star. We found a trend of color at minimum light with a pulsational period that, if taken into account, brings the dispersion in color at minimum light to 0.016 mag for the (r-i), (i-z), and (r-z) colors. These calibrations will be very useful for using RR Lyrae stars from DECam observations as both standard candles for distance determinations and color standards for reddening measurements.
895. C-T1 phot. of NGC 4636 globular cluster system
ID:
ivo://CDS.VizieR/J/A+A/433/43
Title:
C-T1 phot. of NGC 4636 globular cluster system
Short Name:
J/A+A/433/43
Date:
21 Oct 2021
Publisher:
CDS
Description:
Previous smaller-scale studies of the globular cluster system of NGC 4636, an elliptical galaxy in the southern part of the Virgo cluster, have revealed an unusually rich globular cluster system. We re-investigate the cluster system of NGC 4636 with wide-field Washington photometry.
896. CT1 photometry for 11 star fields in the SMC
ID:
ivo://CDS.VizieR/J/MNRAS/451/3219
Title:
CT1 photometry for 11 star fields in the SMC
Short Name:
J/MNRAS/451/3219
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from Washington CT_1_ photometry for 11 star fields located in the western outskirts of the Small Magellanic Cloud (SMC), which cover angular distances to its centre from 2{deg} up to 13{deg} (~2.2-13.8 kpc). The colour-magnitude diagrams, cleaned from the unavoidable Milky Way (MW) and background galaxy signatures, reveal that the most distant dominant main-sequence (MS) stellar populations from the SMC centre are located at an angular distance of ~5.7{deg} (6.1 kpc); no sign of farther clear SMC MS is visible other than the residuals from the MW/background field contamination. The derived ages and metallicities for the dominant stellar populations of the western SMC periphery show a constant metallicity level ([Fe/H]=-1.0 dex) and an approximately constant age value (~7-8 Gyr). Their age-metallicity relationship (AMR) do not clearly differ from the most comprehensive AMRs derived for almost the entire SMC main body. Finally, the range of ages of the dominant stellar populations in the western SMC periphery confirms that the major stellar mass formation activity at the very early galaxy epoch peaked ~7-8 Gyr ago.
897. CT1 photometry in five LMC star clusters
ID:
ivo://CDS.VizieR/J/A+A/501/585
Title:
CT1 photometry in five LMC star clusters
Short Name:
J/A+A/501/585
Date:
21 Oct 2021
Publisher:
CDS
Description:
Aims: We present CCD photometry in the Washington system C and T1 passbands down to T1~22.5 in the fields of NGC 1697, SL 133, NGC 1997, SL 663, and OHSC 28, five mostly unstudied star clusters in the LMC. Methods: Cluster radii were estimated from star counts in appropriate-sized boxes distributed throughout the entire observed fields. We perform a detailed analysis of the field star contamination and derive cluster colour-magnitude diagrams (CMDs). Based on the best fits of isochrones computed by the Padova group to the (T1, C-T_1_) CMDs, the {delta}(T1) index and the Standard Giant Branch procedure, we derive metallicities and ages for the five clusters. We combine our sample with clusters with ages and metallicities on a similar scale and examine relationships between position in the LMC, age and metallicity. Results: With the exception of NGC 1697 (age=0.7Gyr, [Fe/H]=0.0dex), the remaining four clusters are of intermediate-age (from 2.2 to 3.0Gyr) and relatively metal-poor ([Fe/H]=0.7dex). The cluster and field age-metallicty realtions show evidence for a metallicity offset but do overlap, particularly on the upper envelope side of the cluster age-metallicity relation. Conclusions: We confirm previous results that clusters younger than ~1Gyr were formed during an outside-in process; this occurred after a bust of cluster formation that took place mainly in the outer disk and peaked at ~2Gyr ago.
898. C-T1 photometry in NGC 1374, 1379 and 1387
ID:
ivo://CDS.VizieR/J/MNRAS/367/156
Title:
C-T1 photometry in NGC 1374, 1379 and 1387
Short Name:
J/MNRAS/367/156
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a photometric study of the globular cluster systems (GCSs) of the Fornax cluster galaxies NGC 1374, NGC 1379 and NGC 1387. The data consist of images from the wide-field MOSAIC imager of the Cerro Tololo Inter-American Observatory (CTIO) 4-m telescope, obtained with Washington C and Kron-Cousins R filters. The images cover a field of 36x36arcmin^2^, corresponding to 200x200kpc^2^ at the Fornax distance. Two of the galaxies, NGC 1374 and NGC 1379, are low-luminosity ellipticals while NGC 1387 is a low-luminosity lenticular. Their cluster systems are still embedded in the cluster system of NGC 1399. Therefore, the use of a large field is crucial and some differences to previous work can be explained by this. The colour distributions of all GCSs are bimodal. NGC 1387 presents a particularly distinct separation between red and blue clusters and an over-proportionally large population of red clusters. The radial distribution is different for blue and red clusters, red clusters being more concentrated towards the respective galaxies. The different colour and radial distributions point to the existence of two globular cluster subpopulations in these galaxies. Specific frequencies are in the range S_N_=1.4-2.4, smaller than the typical values for elliptical galaxies. These galaxies might have suffered tidal stripping of blue globular clusters by NGC 1399.
899. CT1 photometry in NGC 1399 and NGC 4486
ID:
ivo://CDS.VizieR/J/MNRAS/382/1947
Title:
CT1 photometry in NGC 1399 and NGC 4486
Short Name:
J/MNRAS/382/1947
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper explores the quantitative connection between globular clusters and the diffuse stellar population of the galaxies they are associated with. Both NGC 1399 and NGC 4486 (M87) are well suited for this kind of analysis due to their large globular cluster populations. The main assumption of our Monte Carlo based models is that each globular cluster is formed along with a given diffuse stellar mass that shares the same spatial distribution, chemical composition and age. The main globular cluster subpopulations, that determine the observed bimodal colour distribution, are decomposed avoiding a priori parametric (e.g. Gaussian) fits and using a new colour (C-T1)-metallicity relation. The eventual detectability of a blue tilt in the colour-magnitude diagrams of the blue globular cluster subpopulation is also addressed.
900. CT1 photometry in 6 SMC star clusters
ID:
ivo://CDS.VizieR/J/MNRAS/377/300
Title:
CT1 photometry in 6 SMC star clusters
Short Name:
J/MNRAS/377/300
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present CCD photometry in the Washington C and T1 filters for six star clusters (B 34, NGC 256, NGC 265, NGC 294, IC 1611 and NGC 376) in the Small Magellanic Cloud (SMC) and their surrounding fields. The resultant colour-magnitude diagrams (CMDs) extend from T1~14 to as faint as T1~22 revealing the main-sequence turnoffs of the clusters. Adopting a metallicity of Z=0.004, we compare our cluster photometry with theoretical isochrones in the Washington system in order to derive ages. To facilitate age determination of the surrounding fields, we use the magnitude difference between the helium-burning red clump stars and the main-sequence turnoff. Finally, we estimate mean metallicities for the field stars by comparing the location of the field red giant branch with standard giant branches for Galactic globular clusters of known abundance, corrected for age effects. Combining these results with our previous work, we find a clear trend of younger clusters being located closer to the centre of the SMC. In addition, there is a tendency for the mean metallicity and its dispersion to be greater inside 4{deg} of the SMC's centre as compared to outside this radius. As far as the properties of the field stars are concerned, we find little correlation between the ages of the clusters and those of the field stars against which they are projected. Clearly, more work needs to be done to clarify these trends.