- ID:
- ivo://CDS.VizieR/J/A+A/388/149
- Title:
- CCD Vilnius photometry of M56
- Short Name:
- J/A+A/388/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CCD observations of field stars in an area north-east of the globular cluster M 56 were obtained in six bands of the Vilnius photometric system. The data sets cover a field of 9'x9.5'. An outline of the data pathway from observations to reduction via IRAF is outlined in this text. Photometry of 366 stars brighter than 18th V magnitude has been obtained and the analysis of the observational errors is discussed.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/440/487
- Title:
- Cepheids in the young LMC cluster NGC 1866
- Short Name:
- J/A+A/440/487
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new near-IR light curves for six Cepheids in the young blue LMC cluster NGC 1866 as well as high precision radial velocity curves for ten Cepheids in NGC 1866 and two in NGC 2031. For the six Cepheids in NGC 1866 with new J and K light curves we determine distances and absolute magnitudes by applying the near-IR surface brightness method. We find that the formal error estimates on the derived distances are underestimated by about a factor of two. We find excellent agreement between the absolute magnitudes for the low metallicity LMC Cepheids with the Period-Luminosity (P-L) relation determined by the near-IR surface brightness (ISB) method for Galactic Cepheids suggesting that the slope of the P-L relations for low metallicity and solar metallicity samples could be very similar in contrast to other recent findings. Still there appears to be significant disagreement between the observed slopes of the OGLE based apparent P-L relations in the LMC and the slopes derived from ISB analysis of Galactic Cepheids, and by inference for Magellanic Cloud Cepheids, indicating a possible intrinsic problem with the ISB method itself. Resolving this problem could reaffirm the P-L relation as the prime distance indicator applicable as well to metallicities significantly different from the LMC value.
- ID:
- ivo://CDS.VizieR/J/AJ/119/1268
- Title:
- CFHT adaptive optics observations of M15
- Short Name:
- J/AJ/119/1268
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used an Imaging Fabry-Perot Spectrophotometer with the Adaptive Optics Bonnette on the Canada-France-Hawaii Telescope to measure stellar radial velocities in the globular cluster M15 (NGC 7078). An average seeing of 0.15'' FWHM, with the best-seeing image having 0.09'', allowed us to measure accurately the velocities for five stars within 1'' of the center of M15. Our estimate of the second moment of the velocity distribution (i.e., the dispersion, ignoring rotation) inside a radius of 2'' is 11.5 km.s^-1^, the same value we find out to a radius of about 6''. However, the projected net rotation does increase dramatically at small radii, as our previous observations led us to suspect. The rotation amplitude inside a radius of 3.4'' is v=10.4+/-2.7 km.s^-1^ and the dispersion after removing the rotation is {sigma}=10.3+/-1.4 km.s^-1^, so v/{sigma} {~} 1 in this region. In addition, the position angle of the projected rotation axis differs by 100 degrees from that of the net cluster rotation at larger radii.
- ID:
- ivo://CDS.VizieR/J/ApJ/872/202
- Title:
- CFHT ugi photometry of globular clusters in M85
- Short Name:
- J/ApJ/872/202
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We survey globular clusters (GCs) in M85 using ugi-band images of a 1{deg}x1{deg} field obtained with the MegaCam at the 3.6m Canada-France-Hawaii Telescope. We identify 1318 GC candidates with 20.0mag<g_0_<23.5mag in the entire survey region. Their radial number density profile is well fit by a Sersic profile with n=2.58_-0.33_^+0.43^ and effective radius R_e,GCS_=4.14' (=22kpc), showing that the candidates at R<20' are mostly genuine GCs in M85. We estimate the total number of GCs, N(total)=1216_-50_^+82^, and the specific frequency, S_N_=1.41_-0.06_^+0.10^. The overall color distribution of the GCs in M85 is bimodal, but the GCs in the central region at R<2' do not show a bimodal distribution clearly. The radial number density profile and surface number density map of the blue GCs (BGCs) show more extended structures than those of the red GCs (RGCs). The spatial distributions of both BGCs and RGCs are elongated, similar to that of the galaxy stellar light. The number fraction of the RGCs in the central region is much smaller compared to those in other early-type galaxies of similar luminosity. The mean (g-i)_0_ color of the RGCs in M85 is about 0.1mag bluer than typical values for other Virgo early-type galaxies of similar luminosity, indicating that a significant fraction of the RGCs in M85 may be younger than typical GCs. These results indicate that M85 might have undergone a major wet merger recently.
- ID:
- ivo://CDS.VizieR/J/other/Sci/292.2290
- Title:
- Chandra compact binaries in 47 Tuc
- Short Name:
- J/other/Sci/292.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high-resolution (<~1") deep X-ray images of the globular cluster 47 Tucanae (NGC 104) with the Chandra X-ray Observatory to study the population of compact binaries in the high stellar density core. A 70-kilosecond exposure of the cluster reveals a centrally concentrated population of faint (L_X_~10^30-33^ergs/s) X-ray sources, with at least 108 located within the central 2'x2.5' and >~half with L_X_<~10^30.5^ergs/s. All 15 millisecond pulsars (MSPs) recently located precisely by radio observations are identified, though 2 are unresolved by Chandra. The X-ray spectral and temporal characteristics, as well as initial optical identifications with the Hubble Space Telescope, suggest that >~50 percent are MSPs, about 30 percent are accreting white dwarfs, about 15 percent are main-sequence binaries in flare outbursts, and only two to three are quiescent low-mass X-ray binaries containing neutron stars, the conventional progenitors of MSPs. An upper limit of about 470 times the mass of the sun is derived for the mass of an accreting central black hole in the cluster. These observations provide the first X-ray ``color-magnitude'' diagram for a globular cluster and census of its compact object and binary population. Observations were made on UT 16.31 - 17.22 March, 2000.
- ID:
- ivo://CDS.VizieR/J/ApJ/695/1094
- Title:
- Chandra observations of NGC 4636
- Short Name:
- J/ApJ/695/1094
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the X-ray point-source population in the nearby Virgo elliptical galaxy NGC 4636 from three Chandra X-ray observations. These observations, totaling ~193ks after time filtering, were taken with the Advanced CCD Imaging Camera (ACIS) over a three-year period. Using a wavelet decomposition detection algorithm, we detect 318 individual point sources. For our analysis, we use a subset of 277 detections with >=net 10 counts (a limiting luminosity of approximately 1.2x10^37^erg/s in the 0.5-2keV band, outside the central 1.5' bright galaxy core). We present a radial distribution of the point sources. Between 1.5' and 6' from the center, 25% of our sources are likely to be background sources (active galactic nuclei (AGNs)) and 75% are low-mass X-ray binaries (LMXBs) within the galaxy, while at radial distances greater than 6', background sources (AGN) will dominate the point sources. We find 77 matches between X-ray point sources and globular cluster (GC) candidates found in deep optical images of NGC 4636. In the annulus from 1.5' to 6' of the galaxy center, 48 of the 129 X-ray point sources (37%) with >=10 net counts are matched with GC candidates. Since we expect 25% of these sources to be background AGN, the percentage matched with GCs could be as high as 50%. Of these matched sources, we find that ~70% are associated with the redder GC candidates, those that are thought to have near-solar metal abundance.
- ID:
- ivo://CDS.VizieR/J/ApJ/687/1019
- Title:
- Chandra X-ray observations of M71
- Short Name:
- J/ApJ/687/1019
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observe the nearby, low-density globular cluster M71 (NGC 6838) with the Chandra X-Ray Observatory to study its faint X-ray populations. Five X-ray sources are found inside the cluster core radius, including the known eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light curve of the source coincident with this MSP shows marginal evidence for periodicity at the binary period of 4.2hr. Its hard X-ray spectrum and luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting a similar shock origin of the X-ray emission. A further 24 X-ray sources are found within the half-mass radius, reaching to a limiting luminosity of 1.5x10^30^ergs/s (0.3-8keV). From a radial distribution analysis, we find that 18+/-6 of these 29 sources are associated with M71, somewhat more than predicted, and that 11+/-6 are background sources, both Galactic and extragalactic. M71 appears to have more X-ray sources in the range L_X_=10^30^-10^31^ergs/s than expected by extrapolating from other studied clusters using either mass or collision frequency. We explore the spectra and variability of these sources and describe the results of ground-based optical counterpart searches.
- ID:
- ivo://CDS.VizieR/J/ApJ/657/286
- Title:
- Chandra X-ray sources in M30 (NGC 7099)
- Short Name:
- J/ApJ/657/286
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of six discrete, low-luminosity (LX<10^33^erg/s) X-ray sources, located within 12" of the center of the collapsed-core globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass radius, from a 50ks Chandra ACIS-S exposure.
- ID:
- ivo://CDS.VizieR/J/ApJ/697/224
- Title:
- Chandra X-ray sources in {omega} Cen
- Short Name:
- J/ApJ/697/224
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a ~70ks Chandra Advanced CCD Imaging Spectrometer exposure of the globular cluster {omega} Cen (NGC 5139). The ~17'x17' field of view fully encompasses three core radii and almost twice the half-mass radius. We detect 180 sources to a limiting flux of ~4.3x10^-16^erg/cm^2^/s (L_x_=1.2x10^30^erg/s at 4.9kpc). After accounting for the number of active galactic nuclei and possible foreground stars, we estimate that 45-70 of the sources are cluster members. Four of the X-ray sources have previously been identified as compact accreting binaries in the cluster - three cataclysmic variables (CVs) and one quiescent neutron star. Correlating the Chandra positions with known variable stars yields eight matches, of which five are probable cluster members that are likely to be binary stars with active coronae. Extrapolating these optical identifications to the remaining unidentified X-ray source population, we estimate that 20-35 of the sources are CVs and a similar number are active binaries. This likely represents most of the CVs in the cluster, but only a small fraction of all the active binaries.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/59
- Title:
- Chandra X-ray sources in the globular cluster 47 Tuc
- Short Name:
- J/ApJ/876/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using archival Chandra observations with a total exposure of 510ks, we present an updated catalog of point sources for globular cluster (GC) 47 Tucanae. Our study covers an area of ~176.7'^2^ (i.e., with R<~7.5') with 537 X-ray sources. We show that the surface density distribution of X-ray sources in 47 Tuc is highly peaked in the cluster center, rapidly decreases at intermediate radii, and finally rises again at larger radii, with two distribution dips at R~100" and R~170" for the faint (L_X_>~5.0x10^30^erg/s) and bright (L_X_<~5.0x10^30^erg/s) groups of X-ray sources, respectively. These distribution features are similar to those of blue straggler stars (BSSs), where the distribution dip is located at R~200". By fitting the radial distribution of each group of sources with a "generalized King model", we estimated an average mass of 1.51+/-0.17M_{sun}_, 1.44+/-0.15M_{sun}_ and 1.16+/-0.06M_{sun}_ for the BSSs, bright X-ray sources, and faint X-ray sources, respectively. These results are consistent with the mass segregation effect of heavy objects in GCs, where more massive objects drop to the cluster center faster and their distribution dip propagates outward further. Besides, the peculiar distribution profiles of X-ray sources and BSSs are also consistent with the mass segregation model of binaries in GCs, which suggests that, in addition to the dynamical formation channel, primordial binaries are also a significant contributor to the X-ray source population in GCs.
