CHORIZOS: a CHi-square cOde for parameteRized modelIng and characteriZation of phOtometry and Spectrophotometry

We have developed a CHi-square cOde for parameteRized modelIng and characteriZation of phOtometry and Spectrophotometry (CHORIZOS). CHORIZOS can use up to two intrinsic free parameters (e.g. temperature and gravity for stars; type and redshift for galaxies; or age and metallicity for stellar clusters) and two extrinsic ones (amount and type of extinction). The code uses chi-square minimization to find all models compatible with the observed data in the model N-dimensional (N=1,2,3,4) parameter space. CHORIZOS can use either correlated or uncorrelated colors as input and is especially designed to identify possible parameter degeneracies and multiple solutions. The code is written in IDL and is available to the astronomical community. Here we present the techniques used, test the code, apply it to a few well-known astronomical problems, and suggest possible applications. As a first scientific result from CHORIZOS, we confirm from photometry the need for a revised temperature-spectral type scale for OB stars previously derived from spectroscopy.Comment: 32 pages, 13 figures. To appear in the September 2004 issue of PAS

IMF biases created by binning and unresolved systems

I discuss two of the possible sources of biases in the determination of the IMF: binning and the existence of unresolved components. The first source is important for clusters with a small number of stars detected in a given mass bin while the second one is relevant for all clusters located beyond the immediate solar neighborhood. For both cases I will present results of numerical simulations and I will discuss strategies to correct for their effects. I also present a brief description of a third unrelated bias source.Comment: 6 pages, 10 figures, to appear in "Young massive clusters, initial conditions and environments", typo in author's name correcte

An HST/NICMOS view of the prototypical giant HII region NGC604 in M33

We present the first high-spatial resolution near-infrared (NIR) imaging of NGC 604, obtained with the NICMOS camera aboard the Hubble Space Telescope (HST). These NICMOS broadband images reveal new NIR point sources, clusters, and diffuse structures. We found an excellent spatial correlation between the 8.4 GHz radio continuum and the 2.2mu-m nebular emission. Moreover, massive young stellar object candidates appear aligned with these radio peaks, reinforcing the idea that those areas are star-forming regions. Three different scaled OB associations are recognized in the NICMOS images. The brightest NIR sources in our images have properties that suggest that they are red supergiant stars, of which one of them was previously known. This preliminary analysis of the NICMOS images shows the complexity of the stellar content of the NGC 604 nebula.Comment: Paper presented in the Workshop "Young massive star clusters: initial conditions and environments" (Granada, Spain - Sept 2007). Astrophysics & Space Science in press, 7 pages, 4 figure

Further insights into the structure of 30 Doradus from the Hubble space telescope instruments

New observations with the Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2), combined with prior archival data, provide nearly complete coverage of the inner 30 Doradus Nebula in both nebular lines and continuum at 0″.1 resolution. The developing windblown cavity surrounding the massive first-generation, central cluster and its interface with the remanent molecular clouds, the site of second-generation, triggered star formation, are imaged in their entirety. Dithered Planetary Camera observations with 0″.03 resolution of Knots 1-3 reveal further structural details of the large dust pillars oriented toward the central cluster and the newborn, massive multiple systems of the second generation in those fields. The new data also provide the first WFPC2 coverage of the fields of two interesting, luminous infrared sources observed in our previous Near Infrared Camera and Multi-Object Spectrometer program; comparisons of the high-resolution optical and IR images are illuminating. In addition, we have obtained Space Telescope Imaging Spectrograph optical, long-slit observations of seven O-type multiple systems in the region, including those in Knots 1-3 and four representatives of the older generation. The spatially resolved spectrograms and classifications of the close pairs, with separations ranging from 0″.09 to 1″.18, are presented, as well as WFPC2 photometry of the individual components and the compact clusters of fainter stars associated with them. These new observations, and planned further analysis of them, offer significant new information about the intricate structure and evolution of the two-stage starburst in 30 Dor.Facultad de Ciencias Astronómicas y Geofísica

Further insights into the structure of 30 Doradus from the Hubble space telescope instruments

New observations with the Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2), combined with prior archival data, provide nearly complete coverage of the inner 30 Doradus Nebula in both nebular lines and continuum at 0″.1 resolution. The developing windblown cavity surrounding the massive first-generation, central cluster and its interface with the remanent molecular clouds, the site of second-generation, triggered star formation, are imaged in their entirety. Dithered Planetary Camera observations with 0″.03 resolution of Knots 1-3 reveal further structural details of the large dust pillars oriented toward the central cluster and the newborn, massive multiple systems of the second generation in those fields. The new data also provide the first WFPC2 coverage of the fields of two interesting, luminous infrared sources observed in our previous Near Infrared Camera and Multi-Object Spectrometer program; comparisons of the high-resolution optical and IR images are illuminating. In addition, we have obtained Space Telescope Imaging Spectrograph optical, long-slit observations of seven O-type multiple systems in the region, including those in Knots 1-3 and four representatives of the older generation. The spatially resolved spectrograms and classifications of the close pairs, with separations ranging from 0″.09 to 1″.18, are presented, as well as WFPC2 photometry of the individual components and the compact clusters of fainter stars associated with them. These new observations, and planned further analysis of them, offer significant new information about the intricate structure and evolution of the two-stage starburst in 30 Dor.Facultad de Ciencias Astronómicas y Geofísica

The young stellar population of NGC 4214 as observed with HST. I. Data and methods

We present the data and methods that we have used to perform a detailed UV-optical study of the nearby dwarf starburst galaxy NGC 4214 using multifilter HST/WFPC2+STIS photometry. We explain the process followed to obtain high-quality photometry and astrometry of the stellar and cluster populations of this galaxy. We describe the procedure used to transform magnitudes and colors into physical parameters using spectral energy distributions. The data show the existence of both young and old stellar populations that can be resolved at the distance of NGC 4214 (2.94 Mpc) and we perform a general description of those populations.Comment: 33 pages, 9 figures, and 8 table

Further insights into the structure of 30 Doradus from the Hubble space telescope instruments

New observations with the Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2), combined with prior archival data, provide nearly complete coverage of the inner 30 Doradus Nebula in both nebular lines and continuum at 0″.1 resolution. The developing windblown cavity surrounding the massive first-generation, central cluster and its interface with the remanent molecular clouds, the site of second-generation, triggered star formation, are imaged in their entirety. Dithered Planetary Camera observations with 0″.03 resolution of Knots 1-3 reveal further structural details of the large dust pillars oriented toward the central cluster and the newborn, massive multiple systems of the second generation in those fields. The new data also provide the first WFPC2 coverage of the fields of two interesting, luminous infrared sources observed in our previous Near Infrared Camera and Multi-Object Spectrometer program; comparisons of the high-resolution optical and IR images are illuminating. In addition, we have obtained Space Telescope Imaging Spectrograph optical, long-slit observations of seven O-type multiple systems in the region, including those in Knots 1-3 and four representatives of the older generation. The spatially resolved spectrograms and classifications of the close pairs, with separations ranging from 0″.09 to 1″.18, are presented, as well as WFPC2 photometry of the individual components and the compact clusters of fainter stars associated with them. These new observations, and planned further analysis of them, offer significant new information about the intricate structure and evolution of the two-stage starburst in 30 Dor.Facultad de Ciencias Astronómicas y Geofísica