- ID:
- ivo://CDS.VizieR/J/AJ/101/1699
- Title:
- Photometry in globular cluster NGC 6229
- Short Name:
- J/AJ/101/1699
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD-based BV photometry for over 1100 stars in and around the globular cluster NGC 6229. For the first time, the cluster's entire giant branch and its horizontal branch are delineated, from which metallicity ([Fe/H]~-1.4) and distance (d__{sun}_~28kpc; d_GC_~27kpc) estimates ensue. NGC 6229 is found to have a relatively blue horizontal branch for its intermediate metallicity, which is unusual for an outer halo cluster. Its low R value (defined as N_HB_/N_RG_) hints that the blue color of its horizontal branch is due to a lower than average helium abundance. Three possible new variable stars are identified, including one RR Lyrae and two long-period variables. We present a brief review of our knowledge of basic data for the 13 globular clusters lying more than 24 kpc from the Galactic center. The unusually red horizontal branch phenomenon is common only among the outermost clusters. An average R value for these clusters suggests the effect is not caused by an overabundance of helium. The Oosterhoff dichotomy apparently persists into the outer halo, although the number of clusters with RR Lyrae variables is small.
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- ID:
- ivo://CDS.VizieR/J/AJ/148/27
- Title:
- Photometry in globular clusters. I. NGC 1851
- Short Name:
- J/AJ/148/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The analysis of multiple populations (MPs) in globular clusters (GCs) has become a forefront area of research in astronomy. Multiple red giant branches (RGBs), subgiant branches (SGBs), and even main sequences (MSs) have now been observed photometrically in many GCs, while broad abundance distributions of certain elements have been detected spectroscopically in most, if not all, GCs. UV photometry has been crucial in discovering and analyzing these MPs, but the Johnson U and the Stromgren and Sloan u filters that have generally been used are relatively inefficient and very sensitive to reddening and atmospheric extinction. In contrast, the Washington C filter is much broader and redder than these competing UV filters, making it far more efficient at detecting MPs and much less sensitive to reddening and extinction. Here, we investigate the use of the Washington system to uncover MPs using only a 1 m telescope. Our analysis of the well-studied GC NGC 1851 finds that the C filter is both very efficient and effective at detecting its previously discovered MPs in the RGB and SGB. Remarkably, we have also detected an intrinsically broad MS best characterized by two distinct but heavily overlapping populations that cannot be explained by binaries, field stars, or photometric errors. The MS distribution is in very good agreement with that seen on the RGB, with ~30% of the stars belonging to the second population. There is also evidence for two sequences in the red horizontal branch, but this appears to be unrelated to the MPs in this cluster. Neither of these latter phenomena have been observed previously in this cluster. The redder MS stars are also more centrally concentrated than the blue MS. This is the first time MPs in an MS have been discovered from the ground, and using only a 1 m telescope. The Washington system thus proves to be a very powerful tool for investigating MPs, and holds particular promise for extragalactic objects where photons are limited.
- ID:
- ivo://CDS.VizieR/J/AJ/64/28
- Title:
- Photometry in the globular cluster M22
- Short Name:
- J/AJ/64/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photovisual and photographic magnitudes of more than 400 stars in the globular cluster M22 have been measured. The resulting color-magnitude diagram extends to slightly fainter than the RR Lyurae domain and is generally similar to those for other globular clusters, in particular most resembling the diagram for M13
- ID:
- ivo://CDS.VizieR/J/A+A/525/A19
- Title:
- Photometry of globulars in early galaxies
- Short Name:
- J/A+A/525/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The combination of optical and near-infrared (NIR) colours has the potential to break the age/metallicity degeneracy and offers a better metallicity sensitivity than optical colours alone. Previous studies of extragalactic globular clusters (GCs) with this colour combination, however, have suffered from small samples or have been restricted to a few galaxies. We compile a homogeneous and representative sample of GC systems with multi-band photometry to be used in subsequent papers where ages and metallicity distributions will be studied.
- ID:
- ivo://CDS.VizieR/J/A+A/449/143
- Title:
- Photometry of M31 globular cluster candidates
- Short Name:
- J/A+A/449/143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents accurate spectral energy distributions (SEDs) of 16 M31 globular clusters (GCs) confirmed by spectroscopy and/or high spatial-resolution imaging, as well as 30 M31 globular cluster candidates detected by Mochejska et al., Cat. J/AcA/48/455 (1998). Most of these candidates have m_V_>18, deeper than previous searches, and these candidates have not yet been confirmed to be globular clusters. The SEDs of these clusters and candidates are obtained as part of the BATC Multicolor Survey of the Sky, in which the spectrophotometrically-calibrated CCD images of M31 in 13 intermediate-band filters from 4000 to 10000{AA} were observed. These filters are specifically designed to exclude most of the bright and variable night-sky emission lines including the OH forest. In comparison to the SEDs of true GCs, we find that some of the candidate objects are not GCs in M31. SED fits show that theoretical simple stellar population (SSP) models can fit the true GCs very well. We estimate the ages of these GCs by comparing with SSP models.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A102
- Title:
- Photometry of M31 globular cluster EXT8
- Short Name:
- J/A+A/651/A102
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We recently found the globular cluster (GC) EXT8 in M31 to have an extremely low metallicity of [Fe/H]=-2.91+/-0.04 using high-resolution spectroscopy. Here we present a colour-magnitude diagram (CMD) for EXT8, obtained with the Wide Field Camera 3 on board the Hubble Space Telescope. Compared with the CMDs of metal-poor Galactic GCs, we find that the upper red giant branch (RGB) of EXT8 is about 0.03mag bluer in F606W-F814W and slightly steeper, as expected from the low spectroscopic metallicity. The observed colour spread on the upper RGB is consistent with being caused entirely by the measurement uncertainties, and we place an upper limit of sigma(F606W-F814W)=0.015mag on any intrinsic colour spread. The corresponding metallicity spread can be up to sigma([Fe/H])=0.2dex or >0.7dex, depending on the isochrone library adopted. The horizontal branch (HB) is located mostly on the blue side of the instability strip and has a tail extending to at least M(F606W)=+3, as in the Galactic GC M15. We identify two candidate RR Lyrae variables and several UV-luminous post-HB/post-AGB star candidates, including one very bright (M(F300X)=-3.2) source near the centre of EXT8. The surface brightness of EXT8 out to a radius of 25 arcsec is well fitted by a Wilson-type profile with an ellipticity of epsilon=0.20, a semi-major axis core radius of 0.25", and a central surface brightness of 15.2mag per square arcsec in the F606W band, with no evidence of extra-tidal structure. Overall, EXT8 has properties consistent with it being a "normal", but very metal-poor GC, and its combination of relatively high mass and very low metallicity thus remains challenging to explain in the context of GC formation theories operating within the hierarchical galaxy assembly paradigm.
- ID:
- ivo://CDS.VizieR/J/MNRAS/252/357
- Title:
- Photometry of NGC 6171
- Short Name:
- J/MNRAS/252/357
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- B and V CCD photometry is presented for 1565 stars in the low-concentration globular cluster NGC6171=M107
- ID:
- ivo://CDS.VizieR/J/A+AS/84/59
- Title:
- Photometry of NGC 2808
- Short Name:
- J/A+AS/84/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/AJ/109/269
- Title:
- Photometry of NGC 5053
- Short Name:
- J/AJ/109/269
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present (V,B-V), (V,V-I), and (V,B-I) color-magnitude diagrams for NGC 5053, which is the most metal-poor globular cluster known in the galaxy. The horizontal branch (HB) is predominantly blueward of the RR Lyrae instability strip and the slope of the red giant branch (RGB) is relatively steep, both characteristic of a metal-poor system. Monte- Carlo simulations show that both the RGB and HB are underpopulated relative to those of the metal-poor cluster M15, indicative of the relatively lower total luminosity of NGC 5053. Based on the mean magnitude of stars located at the red and blue edges of the instability strip, we find V(HB) = 16.65 +/- 0.03. At this magnitude, polynomial fits to the cluster RGBs in the two measured colors yield (B-V)_g = 0.71 +/- 0.016 and (V-I)_g = 0.93 +/- 0.016. Using the BVI two-color diagram in a differential manner with respect to M68 and M15 gives a reddening of E(B-V) = 0.06 +/- 0.02 for NGC 5053. We have utilized these quantities to extend the calibration of the simultaneous reddening and metallicity method [Sarajedini, AJ, 107, 618 (1994a)] to [Fe/H] = -2.4. Another feature of the color-magnitude diagram that is evident is the rich population of blue straggler stars (BSSs). We are able to recover 22 of 24 previously known BSSs, and we have added 3 more BSSs.
- ID:
- ivo://CDS.VizieR/J/AJ/105/527
- Title:
- Photometry of RR Lyr stars in LMC cluster NGC 1835
- Short Name:
- J/AJ/105/527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometry is presented for the RR Lyrae variables in the Large Magellanic Cloud (LMC) cluster NGC 1835. Sixteen new variables have been discovered. Due to the extreme crowding of the LMC field stars, the scatter of the light curves and mean magnitudes is greater than that found for other LMC clusters studied under similar conditions. The derived parameters of the light curves yield E(B-V) = 0.13 and [Fe/H] = -1.8, consistent with previous measurements. The complete sample of RR Lyraes has mean magnitudes <V> = 19.38, <B> = 19.70. If a distance modulus of 18.5 mag for the LMC is assumed, then in the mean the NGC 1835 RR Lyraes have <Mv> = 0.48, almost identical to the average found by the same procedure for the six other LMC clusters.
