J. Maíz Apellániz

Instituto De Astrofisica De Andalucia, Granata, Andalusia, Spain

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Publications (91)205.68 Total impact

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    ABSTRACT: Context: Massive stars are extremely important for the chemical evolution of the galaxies; however there are large gaps in our understanding of their properties and formation, mainly because they evolve rapidly, are rare and distant. Recent findings suggest that most O-stars belong to multiple systems. It may well be that almost all massive stars are born as triples or higher multiples, but their large distances require very high angular resolution for a direct detection of the companions at milliarcsecond scales. Aims: Herschel 36 is a young massive system located at 1.3 kpc. It has a combined minimum predicted mass of 45.2 M_sun. Multi-epoch spectroscopic data suggest the existence of three components gravitationally bound. Two of them, system B, are tightly bound in a spectroscopic binary and the third one, component A, orbiting in a wide orbit. Our aim was to image and obtain astrometric and photometric measurements of the component A using, for the first time, long-baseline optical interferometry to further constrain its nature. Methods: We observed Herschel 36 with the near-infrared instrument AMBER attached to the ESO VLT Interferometer, which pro- vides an angular resolution of 2 mas. To perform the interferometric image reconstruction, we used BSMEM. The model fitting to the interferometric observables was done via proprietary routines and LitPro. Results: We imaged the A+B components of Herschel 36 in H and K filters. Component A is located at a projected distance of 1.81 mas, at a position angle of 222 deg. East of North, the flux ratio between components A and B is close to one. The small measured angular separation indicates that the tertiary may be approaching the periastron of its orbit. These results, only achievable with long-baseline near-infrared interferometry, constitute the first step toward a thorough understanding of this massive triple system.
    09/2014;
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    ABSTRACT: Rotation is a key parameter in the evolution of massive stars, affecting their evolution, chemical yields, ionizing photon budget, and final fate. We determined the projected rotational velocity, $v_e\sin i$, of $\sim$330 O-type objects, i.e. $\sim$210 spectroscopic single stars and $\sim$110 primaries in binary systems, in the Tarantula nebula or 30 Doradus (30\,Dor) region. The observations were taken using VLT/FLAMES and constitute the largest homogeneous dataset of multi-epoch spectroscopy of O-type stars currently available. The most distinctive feature of the $v_e\sin i$ distributions of the presumed-single stars and primaries in 30 Dor is a low-velocity peak at around 100\,$\rm{km s^{-1}}$. Stellar winds are not expected to have spun-down the bulk of the stars significantly since their arrival on the main sequence and therefore the peak in the single star sample is likely to represent the outcome of the formation process. Whereas the spin distribution of presumed-single stars shows a well developed tail of stars rotating more rapidly than 300\,$\rm{km s^{-1}}$, the sample of primaries does not feature such a high-velocity tail. The tail of the presumed-single star distribution is attributed for the most part -- and could potentially be completely due -- to spun-up binary products that appear as single stars or that have merged. This would be consistent with the lack of such post-interaction products in the binary sample, that is expected to be dominated by pre-interaction systems. The peak in this distribution is broader and is shifted toward somewhat higher spin rates compared to the distribution of presumed-single stars. Systems displaying large radial velocity variations, typical for short period systems, appear mostly responsible for these differences.
    09/2014;
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    ABSTRACT: The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects.
    08/2014;
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    ABSTRACT: It has been suggested that the compact open cluster VdBH 222 is a young massive distant object. We set out to characterise VdBH 222 using a comprehensive set of multi-wavelength observations. We obtained multi-band optical (UBVR) and near-infrared (JHK) photometry of the cluster field, as well as multi-object and long-slit optical spectroscopy for a large sample of stars in the field. We applied classical photometric analysis, as well as more sophisticated methods using the CHORIZOS code, to determine the reddening to the cluster. We then plotted dereddened HR diagrams and determined cluster parameters via isochrone fitting. We have identified a large population of luminous supergiants confirmed as cluster members via radial velocity measurements. We find nine red supergiants (plus one other candidate) and two yellow supergiants. We also identify a large population of OB stars. Ten of them are bright enough to be blue supergiants. The cluster lies behind 7.5 mag of extinction for the preferred value of Rv of 2.9. Isochrone fitting allows for a narrow range of ages between 12 and 16 Ma. The cluster radial velocity is compatible with distances of 6 and 10 kpc. The shorter distance is inconsistent with the age range and Galactic structure. The longer distance implies an age of 12 Ma and a location not far from the position where some Galactic models place the far end of the Galactic Bar. VdBH 222 is a young massive cluster with a likely mass greater than 20000 Msolar . Its population of massive evolved stars is comparable to that of large associations, such as Per OB1. Its location in the inner Galaxy, presumably close to the end of the Galactic bar, adds to the increasing evidence for vigorous star formation in the inner regions of the Milky Way.
    05/2014;
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    ABSTRACT: We present the second installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ~ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog (GOSC). In this paper we include bright stars and other objects drawn mostly from the first version of GOSC, all of them south of delta = -20 degrees, for a total number of 258 O stars. We also revise the northern sample of paper I to provide the full list of spectroscopically classified Galactic O stars complete to B = 8, bringing the total number of published GOSSS stars to 448. Extensive sequences of exceptional objects are given, including the early Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is also discussed. The magnitude and spatial distributions of the observed sample are analyzed. We also present new results from OWN, a multi-epoch high-resolution spectroscopic survey coordinated with GOSSS that is assembling the largest sample of Galactic spectroscopic massive binaries ever attained. The OWN data combined with additional information on spectroscopic and visual binaries from the literature indicate that only a very small fraction (if any) of the stars with masses above 15-20 M_Sol are born as single systems. In the future we will publish the rest of the GOSSS survey, which is expected to include over 1000 Galactic O stars.
    The Astrophysical Journal Supplement Series 03/2014; 211(1):10-93. · 16.24 Impact Factor
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    ABSTRACT: Detailed spectral classifications are presented for 352 O-B0 stars in the VLT-FLAMES Tarantula Survey, of which 213 O-type are of sufficient quality for further morphological analysis. Among them, six subcategories of special interest are distinguished. (1) Several new examples of the earliest spectral types O2-O3 have been found. (2) A group of extremely rapidly rotating main-sequence objects has been isolated, including the largest $v\sin i$ values known, the spatial and radial-velocity distributions of which suggest ejection from the two principal ionizing clusters. (3) Several new examples of the evolved, rapidly rotating Onfp class show similar evidence. (4) No fewer than 48 members of the Vz category, hypothesized to be on or near the ZAMS, are found in this sample; in contrast to the rapid rotators, they are strongly concentrated to the ionizing clusters, supporting their interpretation as very young objects, as do their relatively faint absolute magnitudes. (5) A surprisingly large fraction of the main-sequence spectra belong to the recently recognized V((fc)) class, with C III emission lines of similar strength to the usual N III in V((f)) spectra; there are also six objects with very high-quality data but no trace of either mission feature, presenting new challenges to physical interpretations. (6) Five spectra with morphologically enhanced nitrogen lines have been detected. Absolute visual magnitudes have been derived for each star with individual extinction laws, and composite HRDs provide evidence of the multiple generations present in this field. Associations with X-ray sources are noted. Further analyses of this unique dataset underway will provide new insights into the evolution of massive stars and starburst clusters.
    02/2014;
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    ABSTRACT: Context: The commonly used extinction laws of Cardelli et al. (1989) have limitations that, among other issues, hamper the determination of the effective temperatures of O and early B stars from optical+NIR photometry. Aims: We aim to develop a new family of extinction laws for 30 Doradus, check their general applicability within that region and elsewhere, and apply them to test the feasibility of using optical+NIR photometry to determine the effective temperature of OB stars. Methods: We use spectroscopy and NIR photometry from the VLT-FLAMES Tarantula Survey and optical photometry from HST/WFC3 of 30 Doradus and we analyze them with the software code CHORIZOS using different assumptions such as the family of extinction laws. Results: We derive a new family of optical+NIR extinction laws for 30 Doradus and confirm its applicability to extinguished Galactic O-type systems. We conclude that by using the new extinction laws it is possible to measure the effective temperatures of OB stars with moderate uncertainties and only a small bias, at least up to E(4405-5495) ~ 1.5 mag.
    Astronomy and Astrophysics 02/2014; · 5.08 Impact Factor
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    ABSTRACT: We analyze spatially resolved, long-slit ultraviolet (UV) and optical stellar spectra of the compact starburst cluster R136 at the core of 30 Doradus. R136 is young and massive, making it an ideal place to study the upper end of the initial mass function. These spectra, taken with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, cover over 100 stars in the inner 4 arcseconds (1 parsec) of R136, a region which cannot be resolved with ground-based spectroscopy. In this poster we present both the UV and optical of over 20 of the brightest stars in R136, extracted with MULTISPEC, a tool written specifically for multiple objects in crowded fields. For each star we present an optical spectral type and a terminal wind velocity derived from the UV data
    01/2014;
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    ABSTRACT: AIMS. We test the hypothesis of O Vz stars (characterized by having HeII4686 stronger in absorption than other He lines in their blue-violet spectra) being at a younger evolutionary stage than are normal O-type dwarfs. METHODS. We have performed a quantitative spectroscopic analysis of a sample of 38 O Vz and 46 O V stars, identified by the VLT-FLAMES Tarantula Survey in the 30 Doradus region of the Large Magellanic Cloud (LMC). We obtained the stellar and wind parameters of both samples using the FASTWIND stellar atmosphere code and the IACOB-GBAT grid-based automatic tool. In the framework of a differential study, we compared the physical and evolutionary properties of both samples, regarding Teff, logg, logQ and logL. We also investigated the predictions of the FASTWIND code about the O Vz phenomenon. RESULTS. We find a differential distribution of objects in terms of effective temperature, with O Vz stars dominant at intermediate values. The O Vz stars in 30 Doradus tend to be younger and less luminous, and they have weaker winds than the O V stars, but we also find examples with ages of 2-4 Myr and with luminosities and winds that are similar to those of normal O dwarfs. Moreover, the O Vz stars do not appear to have higher gravities than the O V stars. In addition to effective temperature and wind strength, our FASTWIND predictions indicate how important it is to take other stellar parameters (gravity and projected rotational velocity) into account for correctly interpreting the O Vz phenomenon. CONCLUSIONS. In general, the O Vz stars appear to be on or very close to the ZAMS, but there are some examples where the Vz classification does not necessarily imply extreme youth. In particular, the presence of O Vz stars in our sample at more evolved phases than expected is likely a consequence of modest O-star winds owing to the low-metallicity environment of the LMC.
    12/2013;
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    ABSTRACT: As part of a photometric campaign of Cyg OB2 carried out with an amateur 35 cm telescope, we discovered a brightening of Cyg OB2-4 B (RA=20:32:13.117, dec=+41:27:24.25 J2000). The star maintained approximately constant magnitudes of RJohnson = 11.23 and IJohnson = 10.47 during the 2012 summer campaign. When the campaign resumed in 4 June 2013 the star retained the previous magnitudes but in a few days it started a progressive brightening that reached RJohnson = 10.66 and IJohnson = 9.78 in late August.
    The Astronomer's Telegram. 11/2013; 5571:1.
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    ABSTRACT: The 30 Doradus (30\,Dor) region in the Large Magellanic Cloud (also known as the Tarantula Nebula) is the nearest massive starburst region, containing the richest sample of massive stars in the Local Group. It is the best possible laboratory to investigate aspects of the formation and evolution of massive stars. Here, we focus on rotation which is a key parameter in the evolution of these objects. We establish the projected rotational velocity, $v_{e}\sin i$, distribution of an unprecedented sample of 216 radial velocity constant ($\rm{\Delta RV\, \leq\, 20 \,km s^{-1}}$) O-type stars in 30\,Dor observed in the framework of the VLT-FLAMES Tarantula Survey (VFTS). The distribution of $v_{e}\sin i$ shows a two-component structure: a peak around 80 $\rm{km s^{-1}}$ and a high-velocity tail extending up to $\sim$600 $\rm{km s^{-1}}$. Around 75% of the sample has 0 $\leq\, v_{e}\sin i \leq$ 200 $\rm{km s^{-1}}$ with the other 25% distributed in the high-velocity tail. The presence of the low-velocity peak is consistent with that found in other studies of late-O and early-B stars. The high-velocity tail is compatible with expectations from binary interaction synthesis models and may be predominantly populated by post-binary interaction, spun-up, objects and mergers. This may have important implications for the nature of progenitors of long-duration gamma ray bursts.
    09/2013;
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    ABSTRACT: Aims. Using ground based multi-object optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to establish the (projected) rotational velocity distribution for a sample of 216 presumably single O-type stars in 30 Doradus (30 Dor). Methods. We measured projected rotational velocities, \vrot, by means of a Fourier transform method and a profile fitting method applied on a set of isolated spectral lines. We also used an iterative deconvolution procedure to infer the probability density, $\rm{P(\veq)}$, of the equatorial rotational velocity, \veq. Results. The distribution of \vrot\ shows a two-component structure: a peak around 80 \kms\ and a high-velocity tail extending up to $\sim$600 \kms. This structure is also present in the inferred distribution $\rm{P(\veq)}$ with around 80% of the sample having 0 $<$ \veq\, $\leq\, 300$ \kms\ and the other 20% distributed in the high-velocity region. Conclusions. Most of the stars in our sample rotate with a rate less than 20%\ of their break-up velocity. For the bulk of the sample, mass-loss in a stellar wind and/or envelope expansion is not efficient enough to significantly spin down these stars within the first few Myr of evolution. The presence of a sizeable population of fast rotators is compatible with recent population synthesis computations that investigate the influence of binary evolution on the rotation rate of massive stars. Despite the fact that we have excluded stars that show significant radial velocity variations, our sample may have remained contaminated by post-interaction binary products. The fact that the high-velocity tail may be preferentially (and perhaps even exclusively), populated by post-binary interaction products, has important implications for the evolutionary origin of systems that produce gamma-ray bursts.
    Astronomy and Astrophysics 09/2013; · 5.08 Impact Factor
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    ABSTRACT: We compile the first comprehensive census of hot luminous stars in the 30 Doradus (30 Dor) star forming region of the LMC. The census extends to a radius of 10arcmin (150pc) from the central cluster, R136. Stars were selected photometrically and combined with the latest spectral types. 1145 candidate hot luminous stars were identified of which >700 were considered genuine early type stars that contribute to feedback. We assess the spectroscopic completeness to be 85% in outer regions (>5pc) but fall to 35% in the vicinity of R136, giving a total of 500 hot luminous stars with spectroscopy. Stellar calibrations and models were used to obtain their physical parameters before integrated values were compared to global observations and the population synthesis code, Starburst99. The 31 W-R and Of/WN stars made large contributions to the total ionising and wind luminosities of ~40% and ~50%, respectively. Stars with Minit>100Msun also showed high contributions to the global feedback, ~25% in both cases. Such massive stars are not accounted for by the current Starburst99 code, which underestimated the ionising and wind luminosities of R136 by factors of ~2 and ~9, respectively. The census inferred a SFR of 0.073+/-0.04Msun/yr for 30 Dor, typically higher than results from popular SFR calibrations. However, it remained consistent with a far-UV luminosity tracer and a combined Halpha and mid-infrared tracer, but only after correcting for Halpha extinction. The global ionising output exceeded measurements from the associated gas and dust, suggesting ~6(+55/-6)% of ionising photons escape the region. When studying very luminous star forming regions, it is therefore essential to include the most massive stars to ensure a reliable energy budget. If 30 Dor is typical of other large star forming regions, estimates of the SFR will be underpredicted if this escape fraction is not accounted for.(abridged)
    Astronomy and Astrophysics 08/2013; · 5.08 Impact Factor
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    ABSTRACT: A census was compiled of all the hot luminous stars within the central 10 arcminutes of 30 Doradus. Candidate hot luminous stars were selected from a series of photometric catalogues, using a set of criteria explained in the paper. All stars meeting this photometric criteria are listed in Tabled1.dat. In addition, Table D1 includes all known Wolf-Rayet and Of/WN stars in the region, which may not have been selected due to photometric effects. Spectral Types were then matched to as many of the candidate stars in Tabled1.dat as possible. Stellar parameters were determined for all stars with the following spectral types: W-R, Of/WN, O-type, B-supergiant, B-giant B1I or earlier, B-dwarf, B0.5V or earlier. These parameters are listed in Tabled2.dat. Parameters of all O-type and B-type stars were derived through various calibrations. Parameters of W-R and Of/WN stars were based on previous work or various template models explained in the paper. (2 data files).
    VizieR Online Data Catalog. 08/2013;
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    ABSTRACT: We present high-quality VLT-FLAMES optical spectroscopy of the nebular gas in the giant star-forming region 30 Doradus. In this paper, the first of a series, we introduce our observations and discuss the main kinematic features of 30 Dor, as revealed by the spectroscopy of the ionized gas in the region. The primary data set consists of regular grid of nebular observations, which we used to produce a spectroscopic datacube of 30 Dor, centered on the massive star cluster R136 and covering a field-of-view of 10'x10'. The main emission lines present in the datacube are from Halpha and [NII]6548,6584. The Halpha emission-line profile varies across the region from simple single-peaked emission to complex, multiple-component profiles, suggesting that different physical mechanisms are acting on the excited gas. To analyse the gas kinematics we fit Gaussian profiles to the observed Halpha features. Unexpectedly, the narrowest Halpha profile in our sample lies close to the supernova remnant 30 Dor B. We present maps of the velocity field and velocity dispersion across 30 Dor, finding five previously unclassified expanding structures. These maps highlight the kinematic richness of 30 Dor (e.g. supersonic motions), which will be analysed in future papers.
    Astronomy and Astrophysics 07/2013; 555:A60. · 5.08 Impact Factor
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    ABSTRACT: The Galactic O-Star Spectroscopic Survey (GOSSS) is obtaining high quality R~2500 blue-violet spectroscopy of all Galactic stars ever classified as of O type with B < 12 and a significant fraction of those with B = 12-14. As of June 2013, we have obtained, processed, and classified 2653 spectra of 1593 stars, including all of the sample with B < 8 and most of the sample with B = 8-10, making GOSSS already the largest collection of high quality O-star optical spectra ever assembled by a factor of 3. We discuss the fraction of false positives (stars classified as O in previous works that do not belong to that class) and the implications of the observed magnitude distribution for the spatial distribution of massive stars and dust within a few kpc of the Sun. We also present new spectrograms for some of the interesting objects in the sample and show applications of GOSSS data to the study of the intervening ISM. Finally, we present the new version of the Galactic O-Star Catalog (GOSC), which incorporates the data in GOSSS-DR1, and we discuss our plans for MGB, an interactive spectral classification tool for OB stars.
    Massive Stars: From α to Ω. 06/2013;
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    ABSTRACT: We are using five different surveys to compile the largest sample of diffuse interstellar band (DIB) measurements ever collected. GOSSS is obtaining intermediate-resolution blue-violet spectroscopy of ~2500 OB stars, of which 60% have already been observed and processed. The other four surveys have already collected multi-epoch high-resolution optical spectroscopy of 700 OB stars with different telescopes, including the 9 m Hobby-Eberly Telescope in McDonald Observatory. Some of our stars are highly-extinguished targets for which no good-quality optical spectra have ever been published. For all of the targets in our sample we have obtained accurate spectral types, measured non-DIB ISM lines, and compiled information from the literature to calculate the extinction. Here we present the first results of the project, the properties of twenty DIBs in the 4100-5500 {\AA} range. We clearly detect a couple of previously elusive DIBs at 4170 {\AA} and 4591 {\AA}; the latter could have coronene and ovalene cations as carriers.
    IAU Symposium 297 on The Diffuse Interstellar Bands; 05/2013
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    ABSTRACT: Massive stars are of fundamental importance for almost all aspects of astrophysics, but there still exist large gaps in our understanding of their properties and formation because they are rare and therefore distant. It has been found that most O-stars are multiples. HD 150 136 is the nearest system to Earth with >100 M_sol, and provides a unique opportunity to study an extremely massive system. Recently, evidence for the existence of a third component in HD 150 136, in addition to the tight spectroscopic binary that forms the main component, was found in spectroscopic observations. Our aim was to image and obtain astrometric and photometric measurements of this component using long baseline optical interferometry to further constrain the nature of this component. We observed HD150136 with the near-infrared instrument AMBER attached to the ESO VLT Interferometer. The recovered closure phases are robust to systematic errors and provide unique information on the source asymmetry. Therefore, they are of crucial relevance for both image reconstruction and model fitting of the source structure. The third component in HD 150 136 is clearly detected in the high-quality data from AMBER. It is located at a projected angular distance of 7.3 mas, or about 13 AU at the line-of-sight distance of HD 150 136, at a position angle of 209 degrees East of North, and has a flux ratio of 0.25 with respect to the inner binary. We resolved the third component of HD 150 136 in J, H and K filters. The luminosity and color of the tertiary agrees with the predictions and shows that it is also an O main-sequence star. The small measured angular separation indicates that the tertiary may be approaching the periastron of its orbit. These results, only achievable with long baseline near infrared interferometry, constitute the first step towards the understanding of the massive star formation mechanisms.
    Astronomy and Astrophysics 05/2013; 554:l4. · 5.08 Impact Factor
  • J. Maíz Apellániz
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    ABSTRACT: I consider whether we can significantly improve the Cardelli et al. te{Cardetal89} family of extinction laws using new data and techniques. There are six different aspects that need to be treated: The use of monochromatic quantities, the three different wavelength regimes (NIR, optical and UV), the sample, and the photometric calibration. Excluding the behavior in the NIR and UV, I discuss the other four aspects and propose a new family of extinction laws derived from VLT/FLAMES and HST/WFC3 data.
    05/2013;
  • J. Maíz Apellániz
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    ABSTRACT: The last two decades have produced a proliferation of stellar atmosphere grids, evolutionary tracks, and isochrones which are available to the astronomical community from different internet services. However, it is not straightforward (at least for an inexperienced user) to manipulate those models to answer questions of the type: What is the spectral energy distribution of a 9000 K giant? What about its J-band magnitude for different metallicities? What can I tell about the mass of a star if I know that its unreddened B-V color is -0.05 and its luminosity in solar units is 10^5? The answers to those questions are indeed in the models but a series of transformations and combinations involving different variables and models are required to obtain them. To make the available knowledge more user friendly, I have combined a number of state-of-the-art sources to create a 3-D (effective temperature, luminosity, and metallicity) grid of stellar models for which I provide calibrated SEDs and magnitudes as well as auxiliary variables such as mass and age. Furthermore, I have generated a grid of extinguished magnitudes using the recent Maíz Apellániz et al. (2012) extinction laws and incorporated them into the Bayesian code CHORIZOS (Maíz Apellániz 2004).
    05/2013;

Publication Stats

399 Citations
205.68 Total Impact Points

Institutions

  • 2006–2014
    • Instituto De Astrofisica De Andalucia
      Granata, Andalusia, Spain
  • 2001–2010
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
  • 2008
    • Instituto Argentino de Radioastronomía
      Buenos Aires, Buenos Aires F.D., Argentina