1,721,086 research outputs found
STEP: Dissecting the SMC with the VLT Survey Telescope
Full text linkWe present the stellar catalog of g, r, i, H-alpha photometry from our survey STEP (SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy), a VST (the ESO VLT Survey Telescope) campaign of 53 deg2 dedicated to the study of the main body of the Small Magellanic Cloud and the Magellanic Bridge. Our photometry is able to resolve individual stars down to magnitudes well below the main-sequence turn-off of the oldest populations. We report some key results, including the detection of a prominent burst of star formation, which occurred in the SMC about 100-200 Myr ago, and the confirmation of a bimodal Red-Clump, evidence of a complex interaction history between the Clouds
Dissecting 30 Doradus: Optical and Near Infrared Star Formation History of the starburst cluster NGC2070 from the Hubble Tarantula Treasury Project
No full textI will present new results on the star formation history of 30 Doradus
in the Large Magellanic Cloud based on the panchromatic imaging survey
Hubble Tarantula Treasury Project (HTTP). Here the focus is on the
starburst cluster NGC2070. The star formation history is derived by
comparing the deepest ever optical and NIR color-magnitude diagrams
(CMDs) with state-of-the-art synthetic CMDs generated with the latest
PARSEC models, which include all stellar phases from pre-main sequence
to post-main sequence. For the first time in this region we are able to
measure the star formation using intermediate and low mass stars
simultaneously. Our results suggest that NGC2070 experienced a prolonged
activity. I will discuss the detailed star formation history, initial
mass function and reddening distribution
Star Formation Histories of Dwarf Galaxies from the Colour-Magnitude Diagrams of Their Resolved Stellar Populations
Full text linkIn this tutorial paper we summarize how the star formation (SF) history of a galactic region can be derived from the colour-magnitude diagram (CMD) of its resolved stars. The procedures to
build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. To summarize: (1) only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather continuous, or gasping, SF regimes; (2) a few early-type dwarfs have experienced only one episode of SF activity concentrated at the earliest epochs, whilst many others show extended or recurrent SF activity; (3) no galaxy experiencing now its first SF episode has been found yet; (4) no frequent evidence of strong SF bursts is found; (5) there is no significant difference in the SFH of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these results on the galaxy formation scenarios are briefly discussed
The old open clusters Berkeley 32 and King 11
Full text linkWe have obtained CCD BVI imaging of the old open clusters Berkeley 32 and King 11. Using the synthetic colour-magnitude diagram method with three different sets of stellar evolution models of various metallicities, with and without overshooting, we have determined their age, distance, reddening and indicative metallicity, as well as distance from the Galactic Centre and height from the Galactic plane. The best parameters derived for Berkeley 32 are: subsolar metallicity (Z = 0.008 represents the best choice, Z = 0.006 or 0.01 is more marginally acceptable), age = 5.0-5.5 Gyr (models with overshooting; without overshooting the age is 4.2-4.4 Gyr with poorer agreement), (m -M)(0)= 12.4-12.6, E(B -V) = 0.12-0.18 (with the lower value being more probable because it corresponds to the best metallicity), R-GC similar to 10.7-11 kpc and vertical bar Z vertical bar similar to 231-254 pc. The best parameters for King 11 are: Z= 0.01, age = 3.5-4.75 Gyr, (m -M)(0)= 11.67-11.75, E(B -V) = 1.03-1.06, R-GC similar to 9.2-10 kpc and vertical bar Z vertical bar similar to 253-387 pc
Restoring color-magnitude diagrams with the Richardson-Lucy algorithm
No full textAims. We present an application of the Richardson-Lucy algorithm to the analysis of color-magnitude diagrams by converting the CMD into an image and using a restoring point spread function function (psf) derived from the known, often complex, sources of error. Methods. We show numerical experiments that demonstrate good recovery of the original image and establish convergence rates for ideal cases with single Gaussian uncertainties and poisson noise using a chi(2) statistic. About 30-50 iterations suffice. As an application, we show the results for a particular case, the Hipparcos sample of the solar neighborhood where the uncertainties are mainly due to parallax which we model with a composite weighted Gaussian using the observed error distributions. The resulting psf has a slightly narrower core and broader wings than a single Gaussian. The reddening and photometric errors are considerably reduced by restricting the sample to within 80 pc and to M-V <= 3.5. Results. We find that the recovered "image", which has a narrower, better defined main sequence and a more clearly defined red giant clump, can be used as input to stellar evolution modeling of the star formation rate in the solar vicinity and, with more contributing uncertainties taken into account, for general Galactic and extragalactic structure and population studies
Star formation and environment: a step in understanding the formation and evolution of local dwarf galaxies
No full textWe present here the results obtained from studying the resolved stellar populations of two dwarf irregular galaxies in the nearby Universe. These galaxies, DDO 68 and NGC 4449, were studied within the Legacy ExtraGalactic UV Survey, an HST program aimed to uncover the many ways in which the star formation (SF) process occurs at different scales. Thanks to the deep photometry obtained in different bands (from λ2704 Å to λ8057 Å), we were able to connect the location and timescales of the star forming regions within the galaxies to merging and interaction with gas clouds and satellites, a crucial aspect of galaxy evolution, even in such small systems. From the color-magnitude diagrams of the analyzed galaxies we were able to recover their star formation history (up to ~ 2 - 3 Gyr ago since we do not observe the oldest main sequence turn-off or horizontal branch, due to the systems' distance), finding that the SF never really stopped, but proceeded continuously even with the succession of high and low activity. The time intervals where we find higher SF rates in the two galaxies well agree with the dynamical timescales of previous interactions events, which might represent a major channel for triggering the SF in relatively isolated galaxies
NGC 1817, NGC 2141 and Berkeley 81: three BOCCE clusters of intermediate age
Full text linkIn this paper we analyse the evolutionary status of three open clusters: NGC 1817, NGC 2141 and Berkeley 81. They are all of intermediate age, two are located in the Galactic anticentre direction while the third one is located in the Galactic Centre direction. All of them were observed with Large Binocular Camera at Large Binocular Telescope using the Bessel B, V and I filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram (CMD) method, i.e. the direct comparison of the observational CMDs with a library of synthetic CMDs generated with different evolutionary sets (Padova, FRANEC and FST). This analysis shows that NGC 1817 has subsolar metallicity, age between 0.8 and 1.2 Gyr, reddening E(B - V) in the range 0.21 and 0.34 and distance modulus (m - M)(0) of about 10.9; NGC 2141 is older, with age in the range 1.25 and 1.9 Gyr, E(B - V) between 0.36 and 0.45, (m - M)(0) between 11.95 and 12.21 and subsolar metallicity; Berkeley 81 has metallicity about solar, with age between 0.75 and 1.0 Gyr, has reddening E(B - V) similar to 0.90 and distance modulus (m - M)(0) similar to 12.4. Exploiting the large field of view of the instrument we derive the structure parameters for NGC 2141 and Berkeley 81 by fitting a King profile to the estimated density profile. Combining this information with the synthetic CMD technique we estimate a lower limit for the cluster total mass for these two systems
The anticentre old open clusters Berkeley 27, Berkeley 34 and Berkeley 36: new additions to the BOCCE project
Full text linkIn this paper, we present the investigation of the evolutionary status of three open clusters: Berkeley 27, Berkeley 34 and Berkeley 36, all located in the Galactic anticentre direction. All of them were observed with SUperb Seeing Imager 2 at the New Technology Telescope using the Bessel B, V and I filters. The cluster parameters have been obtained using the synthetic colourmagnitude diagram (CMD) method, i.e. the direct comparison of the observational CMDs with a library of synthetic CMDs generated with different evolutionary sets (Padova, FRANEC and FST). This analysis shows that Berkeley 27 has an age between 1.5 and 1.7 Gyr, a reddening E(B-V) in the range 0.400.50 and a distance modulus (m-M)0 between 13.1 and 13.3; Berkeley 34 is older with an age in the range 2.12.5 Gyr, E(B-V) between 0.57 and 0.64 and (m-M)0 between 14.1 and 14.3; Berkeley 36, with an age between 7.0 and 7.5 Gyr, has a reddening of E(B-V) similar to 0.50 and a distance modulus (m-M)0 between 13.1 and 13.2. For all the clusters, our analysis suggests a subsolar metallicity in accord with their position in the outer Galactic disc
- …
