Abstract
The VISTA Magellanic Cloud (VMC; PI: M.-R. L. Cioni) survey is collecting deep K
s-band time series photometry of the pulsating variable stars hosted by the system formed by the two ...Magellanic Clouds (MCs) and the bridge connecting them. In this paper, we present the first results for classical Cepheids, from the VMC observations of two fields in the Large Magellanic Cloud (LMC), centred on the South Ecliptic Pole and the 30 Doradus star-forming regions, respectively. The VMC K
s-band light curves of the Cepheids are well sampled (12 epochs) and of excellent precision (typical errors of ∼0.01 mag). We were able to measure for the first time the K
s magnitude of the faintest classical Cepheids in the LMC (K
s ∼ 17.5 mag), which are mostly pulsating in the first overtone (FO) mode, and to obtain FO period-luminosity (PL), period-Wesenheit (PW) and period-luminosity-colour (PLC) relations, spanning the full period range from 0.25 to 6 d. Since the longest period Cepheid in our data set has a variability period of 23 d, we have complemented our sample with literature data for brighter F Cepheids. On this basis, we have built a PL relation in the K
s band that, for the first time, includes short-period - hence low-luminosity - pulsators, and spans the full range from 1.6 to 100 d in period.We also provide the first ever empirical PW and PLC relations using the (V − K
s) colour and time series K
s photometry. The very small dispersion (∼0.07 mag) of these relations makes them very well suited to study the three-dimensional geometry of the Magellanic system. The use of 'direct' (parallax- and Baade-Wesselink-based) distance measurements to both Galactic and LMC Cepheids allowed us to calibrate the zero-points of the PL, PW and PLC relations obtained in this paper, and in turn to estimate an absolute distance modulus of (m − M)0 = 18.46 ± 0.03 mag for the LMC. This result is in agreement with most of the latest literature determinations based on classical Cepheids.
The Large Magellanic Cloud (LMC) star cluster system offers the unique opportunity to independently check the accuracy of age (and the corresponding mass) determinations based on a number of ...complementary techniques. Using our sophisticated tool for star cluster analysis based on broad-band spectral energy distributions (SEDs), ‘AnalySED’, we re-analyse the Hunter et al. LMC cluster photometry. Our main aim is to set the tightest limits yet on the accuracy of absolute age determinations based on broad-band SEDs, and therefore on the usefulness of such an approach. Our broad-band SED fits yield reliable ages, with statistical absolute uncertainties within Δlog(Age/yr) ≃ 0.4 overall. The systematic differences we find with respect to previous age determinations are caused by conversions of the observational photometry to a different filter system, thus leading to systematically inaccurate results. The LMC's cluster formation rate (CFR) has been roughly constant outside of the well-known age gap between ∼3 and 13 Gyr, when the CFR was a factor of ∼5 lower. Using a simple approach to derive the characteristic cluster disruption time-scale, we find that , where . This long characteristic disruption time-scale implies that we are observing the initial cluster mass function (CMF). We conclude that while the older cluster (sub)samples show CMF slopes that are fully consistent with the α≃-2 slopes generally observed in young star cluster systems, the youngest mass and luminosity-limited LMC cluster subsets show shallower slopes (at least below masses of a few ×103 M⊙), which is contrary to dynamical expectations. This may imply that the initial CMF slope of the LMC cluster system as a whole is not well represented by a power law, although we cannot disentangle the unbound from the bound clusters at the youngest ages.
The UKIDSS Galactic Plane Survey Lucas, P. W.; Hoare, M. G.; Longmore, A. ...
Monthly notices of the Royal Astronomical Society,
11/2008, Letnik:
391, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The UKIDSS Galactic Plane Survey (GPS) is one of the five near-infrared Public Legacy Surveys that are being undertaken by the UKIDSS consortium, using the Wide Field Camera on the United Kingdom ...Infrared Telescope. It is surveying 1868 deg2 of the northern and equatorial Galactic plane at Galactic latitudes −5° < b < 5° in the J, H and K filters and a ∼200-deg2 area of the Taurus–Auriga–Perseus molecular cloud complex in these three filters and the 2.12 μm (1–0) H2 filter. It will provide data on ∼2 × 109 sources. Here we describe the properties of the data set and provide a user's guide for its exploitation. We also present brief Demonstration Science results from DR2 and from the Science Verification programme. These results illustrate how GPS data will frequently be combined with data taken in other wavebands to produce scientific results. The Demonstration Science comprises six studies. (1) A GPS-Spitzer-GLIMPSE cross-match for the star formation region G28.983−0.603 to identify YSOs. This increases the number of YSOs identified by a factor of 10 compared to GLIMPSE alone. (2) A wide-field study of the M17 nebula, in which an extinction map of the field is presented and the effect of source confusion on luminosity functions in different subregions is noted. (3) H2 emission in the ρ Ophiuchi dark cloud. All the molecular jets are traced back to a single active clump containing only a few protostars, which suggests that the duration of strong jet activity and associated rapid accretion in low-mass protostars is brief. (4) X-ray sources in the nuclear bulge. The GPS data distinguishes local main-sequence counterparts with soft X-ray spectra from nuclear bulge giant counterparts with hard X-ray spectra. (5) External galaxies in the zone of avoidance. The galaxies are clearly distinguished from stars in fields at longitudes l > 90°. (6) IPHAS-GPS optical–infrared spectrophotometric typing. The (i′−J) versus (J−H) diagram is used to distinguish A–F type dwarfs, G dwarfs, K dwarfs and red clump giants in a field with high reddening.
Abstract
Simple stellar population (SSP) synthesis models are useful tools for studying the nature of unresolved star clusters in external galaxies. However, the plethora of currently available SSP ...models gives rise to significant and poorly documented systematic differences. Here we consider the outputs of the commonly used Bruzual & Charlot and GALaxy EVolution (GALEV) models, as well as a recently updated SSP model suite which attempts to include the contributions of binary merger products in the form of blue straggler stars (BS-SSP). We rederive the ages, metallicities, extinction values and masses of 445 previously observed globular-like clusters in M31 based on χ2 minimization of their spectral energy distributions with respect to these three different SSP models by adopting a Chabrier-like stellar initial mass function. A comparison between our new results and previous estimates of the same parameters shows that the Bruzual & Charlot models yield the youngest ages and lowest masses, while adoption of the BS-SSP models results in the oldest ages and highest mass estimates. Similarly, the GALEV SSP models produce the lowest metallicities, with the highest values resulting from the BS-SSP model suite. These trends are caused by intrinsic differences associated with the models and are not significantly affected by the well-known age-metallicity degeneracy. Finally, we note that the mass function of the massive M31 star clusters is similar to that of the Milky Way's globular clusters, which implies that the two star cluster systems likely formed under similar environmental conditions.
We analyse the global structure of the old stellar discs in 34 edge-on spiral galaxies. The radial and vertical exponential scale parameters of the discs are obtained by applying an improved ...two-dimensional decomposition technique to our I-band photometry. We find a clear increase in the disc scaleheight with maximum rotational velocity, in accordance with observations of the stellar velocity dispersions in galaxy discs. The range and maximum of the intrinsic flattening of the disc light seem to increase with both maximum rotational velocity and total Hi mass. We use the disc flattening to estimate the disc contribution to the maximum rotational velocity, resulting in an average of 57 ± 22 per cent. The disc light distributions are further investigated for the presence of radial truncations. We find that the radial light distributions of at least 20 spirals are truncated, corresponding to 60 per cent of the sample. For small scalelength spirals, which are the most numerous in the local Universe, the results suggest that the average ratio of disc truncation radius to disc scalelength is at least four.
We present a catalogue of 1768 eclipsing binary stars (EBs) detected in the Large Magellanic Cloud (LMC) by the second generation of the EROS survey (hereinafter EROS-2); 493 of them are new ...discoveries located in outer regions (out of the central bar) of the LMC. These sources were originally included in a list of candidate classical Cepheids (CCs) extracted from the EROS-2 catalogue on the basis of the period (0.89 < P
EROS < 15.85 d) versus luminosity 13.39 < 〈B
EROS〉 < 17.82 mag diagram. After visual inspection of the light curves we reclassified them as eclipsing binaries. They have blue colours (B
EROS − R
EROS < 0.2 mag) hence we classed them as hot eclipsing binaries (HEBs) containing hot massive components: main sequence (MS) stars or blue giants. We present K
s-band light curves for 999 binaries from our sample that have a counterpart in the VISTA near-infrared ESO public survey of the Magellanic Clouds system (VMC). We provide spectral classifications of 13 HEBs with existing spectroscopy. We divided our sample into contact-like binaries and detached/semi-detached systems based on both visual inspection and the parameters of the Fourier decomposition of the light curves and analysed the period–luminosity (PL) relations of the contact-like systems using the R
EROS and K
s magnitudes at maximum light. The contact-like binaries in our sample do not follow PL relations. We analysed the sample of contact binaries from the OGLE III catalogue and confirmed that PL
I
and
${\rm PL}_{K_{\rm s}}$
sequences are defined only by eclipsing binaries containing a red giant component.
Stellar clusters are regularly used to study the evolution of their host galaxy. Except for a few nearby galaxies, these studies rely on the interpretation of integrated cluster properties, ...especially integrated photometry observed using multiple filters (i.e., the spectral energy distribution, SED). To allow interpretation of such observations, we present a large set of GALEV cluster models using the realistic approach of adopting stochastically sampled stellar initial mass functions. We provide models for a wide range of cluster masses (10 super(3)-2 x 10 super(5) M sub(middot in circle)), metallicities (-2.3 < or =, slant Fe/H < or =, slant +0.18 dex), foreground extinction, and 184 regularly used filters. We analyze various sets of stochastic cluster SEDs by fitting them with non-stochastic models, which is the procedure commonly used in this field. We identify caveats and quantify the fitting uncertainties associated with this standard procedure. We show that this can yield highly unreliable fitting results, especially for low-mass clusters.
We present K
s-band light curves for 299 Cepheids in the Small Magellanic Cloud (SMC) of which 288 are new discoveries that we have identified using multi-epoch near-infrared photometry obtained by ...the VISTA survey of the Magellanic Clouds system (VMC). The new Cepheids have periods in the range from 0.34 to 9.1 d and cover the magnitude interval 12.9 ≤ 〈K
s〉 ≤ 17.6 mag. Our method was developed using variable stars previously identified by the optical microlensing survey OGLE. We focus on searching new Cepheids in external regions of the SMC for which complete VMC K
s-band observations are available and no comprehensive identification of different types of variable stars from other surveys exists yet.
We derive the proper motions, membership probabilities, and velocity dispersions of stars in the regions of the young (~2-4 Myr old) open clusters NGC 2244 (the central cluster in the Monoceros R2 ...association) and NGC 6530 (the dominant cluster in the Sgr OB1 association) from photographic plate material obtained at Shanghai Astronomical Observatory, with time baselines of 34 and 87 yr, respectively. Both clusters show clear evidence of mass segregation, but they do not exhibit any significant velocity-mass (or, equivalently, velocity-luminosity) dependence. This provides strong support for the suggestion that the observed mass segregation is at least partially due to the way in which star formation has proceeded in these complex star-forming regions ('primordial' mass segregation). Based on arguments related to the clusters' published initial mass functions, in conjunction with our new measurements of their internal velocity dispersions (~35 and 8 km s-1 for NGC 2244 and NGC 6530, respectively), we provide strong arguments in favor of the dissolution of NGC 2244 on very short timescales, while we speculate that NGC 6530 may be more stable against the effects of internal two-body relaxation. However, this latter object may well be destroyed by the strong tidal field prevalent at its location in the Galactic plane in the direction of the Galactic center.
The VMC survey Tatton, B L; van Loon, J Th; Cioni, M-R ...
Astronomy and astrophysics (Berlin),
06/2013, Letnik:
554
Journal Article
Recenzirano
The details of how galaxies have evolved over cosmological times are imprinted in their star formation history, chemical enrichment and morpho-kinematic structure. Parameters behind these, such as ...effective temperature and metallicity, can be measured by combining photometric techniques with modelling. In this paper we present a detailed reddening map of the central 30 Doradus region of the Large Magellanic Cloud; for both community use and as a test of the methods used for future use on a wider area. The reddening, a measurement of dust extinction, acts as a tracer of the interstellar medium (ISM). This new reddening map shows correlation with equivalent maps in the literature, validating the method of red clump star selection. We make our reddening map available for community use. In terms of ISM the red clump stars appear to be more affected by the cooler dust measured by 70 mu m emission because there is stronger correlation between increasing emission and extinction due to red clump stars not being located near hot stars that would heat the dust.
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