• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.535-537
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• 2015

Interpreting ultraviolet-to-infrared (UV-to-IR) observations of galaxies in terms of constraints on physical parameters-such as stellar mass ($M_{\ast}$) and star formation rate (SFR)-requires spectral synthesis modelling. We investigate how increasing the level of sophistication of the standard simplifying assumptions of such models can improve estimates of galaxy physical parameters. To achieve this, we compile a sample of 1048 galaxies at redshifts 0.7 < z < 2.8 with accurate photometry at rest-frame UV to near-IR wavelengths from the 3D-HST Survey. We compare the spectral energy distributions of these galaxies with those from different model spectral libraries to derive estimates of the physical parameters. We find that spectral libraries including sophisticated descriptions of galaxy star formation histories (SFHs) and prescriptions for attenuation by dust and nebular emission provide a much better representation of the observations than 'classical' spectral libraries, in which galaxy SFHs are assumed to be exponentially declining functions of time, associated with a simple prescription for dust attenuation free of nebular emission. As a result, for the galaxies in our sample, $M_{\ast}$ derived using classical spectral libraries tends to be systematically overestimated and SFRs systematically underestimated relative to the values derived adopting a more realistic spectral library. We conclude that the sophisticated approach considered here is required to reliably interpret fundamental diagnostics of galaxy evolution.

• Journal of The Korean Astronomical Society
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• v.21 no.1
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• pp.57-65
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• 1988

The absolute measurements of fluxes in the region ${\lambda}{\lambda}3,100-8,090\;{\AA}$ emitted in the visible continua of some galactic Wolf-Rayet stars are presented. These observations were made by a two-channel scanner which was built up cooperatively by the Observatoire of Lyon and the Laboratoire d'Astronomie Spatiale. The fluxes, dereddened from those data, were combined with IUE and ANS ultraviolet measurements. These fluxes were compared with those of LTE plane paralleled model atmospheres of Kurucz (1979) and were also integrated in order to derive effective temperatures and bolometric corrections for the program stars. The derived effective temperatures and bolometric corrections for the stars were in the range of $25,000\;K{\sim}32,700\;K$, and of $-2.5\;mag.{\sim}-3.7\;mag.$, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.79.2-79.2
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• 2013

The distributions of Horizontal Branch (HB) star color, temperature, and mass encode a great deal of information on the stellar evolutionary and (possibly) dynamical processes taking place in Globular Clusters (GCs). An accurate physical modeling of the Red Giant Branch (RGB) mass-loss process is key to solving the so-called second parameter problem. In my poster I will present the most recent advancements of an analytical model for mass-loss along the RGB. The model predicts the HB mass distribution with remarkable accuracy over a sample of 4 GCs. These results were submitted as a paper to ApJ (Pasquato et al. 2013, ApJ submitted), but here I expand on them presenting refinements to the model and a comparison with HB masses obtained from Galex ultraviolet observations.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.64.1-64.1
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• 2014

We study the dust and star-formation characteristics of a nearby dwarf elliptical galaxy, NGC 855. With various archival data from ultraviolet to far-infrared, we build up the spectral energy distribution (SED) that can give us constraints on stellar populations, dust characteristics, star-formation history, etc. From GALEX and SDSS data, slightly de-centered bluer central core is confirmed, where star formation might take place. This regions is coincident with seemingly dis-integrated cores detected by Spitzer IRAC data and with bright Ha feature observed at ground-based telescope. The PACS and SPIRE data by Herschel Space Observatory show the dominant dust features at the center. Lastly, we propose necessary follow-up observations with ground-based telescopes to investigate spectral properties of NGC 855.

• Publications of The Korean Astronomical Society
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• v.9 no.1
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• pp.111-166
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• 1994

I have developed a UV and visible spectroscopic database (UVSD) for atoms and molecules, which are found in interstellar medium, stars, galaxies, and in the atmospheres of the earth, planets, satellites, and comets. This UV and visible database, which is machine-readable, consists of three different sub-databases depending upon the characteristics of the sub-databases: (A) atomic and molecular line listings from laboratory observations or theoretical studies; (B) absorption spectra measured in laboratories; and (C) solar UV, visible, and infrared spectral atlases. The UVSD is in a very initial stage of development compared with other well organized and established infrared and microwave databases. In order to make a good quality and complete database, substantial efforts should be made for the acquisition of scattered important data from laboratories or institutions, and then the acquired heterogeneous data should be peer-reviewed and standardized.

• The Bulletin of The Korean Astronomical Society
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• v.34 no.2
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• pp.78.1-78.1
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• 2009

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.67.1-67.1
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• 2011

Recent observations and modeling of globular clusters with multiple populations strongly indicate the presence of super helium-rich subpopulations in old stellar systems. Motivated by this, we have constructed new population synthesis models with and without helium-enhanced subpopulations to investigate their impact on the UV-upturn phenomenon of quiescent early-type galaxies. We find that our models with helium-enhanced subpopulations can naturally reproduce the strong UV-upturns observed in giant elliptical galaxies assuming an age similar to that of old globular clusters in the Milky Way. The major source of far-UV (FUV) flux, in this model, is relatively metal-poor and helium-enhanced hot horizontal branch stars and their progeny. The Burstein et al. (1988) relation of the FUV - V color with metallicity is also explained either by the variation of the fraction of helium-enhanced subpopulations or by the spread in mean age of stellar populations in early-type galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.71.1-71.1
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• 2011

Significant discrepancies have been found between the dust masses of edge-on spiral galaxies derived from various tracers (optical/near-infrared, far-infrared/sub-millimeter observations, and the variation of dust attenuation with viewing angle). Here we report the first detection of a vertically extended far-ultraviolet (FUV) and near-UV (NUV) emission in an edge-on spiral galaxy NGC 891. The vertically extended emission is interpreted as the dust-scattered light due to a extraplanar dust layer in NGC 891 that contains about the same mass as the standard thin dust disk. This new dust component completely encloses the stellar disk and bulge, and solves the puzzle of dust mass.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.60.2-60.2
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• 2014

The dust cloud around ${\lambda}$-Orionis is seen to be circular symmetric with the large angular extent (${\sim}8^{\circ}$). However, whether the three dimensional structure of the cloud is shell or torus ring is not yet fully resolved. We studied the structure of the dust cloud using a three-dimensional Monte-Carlo simulation code, MoCafe (Monte Carlo radiative transfer). The dust density structure of the cloud was inferred based on the star-count method. We assumed that the cloud is a spherical shell or a torus ring and calculated the radial profiles of scattered light originating from a central OB association. Comparison of the results with the S2/68 ultraviolet observations indicates that the cloud is a spherical shell. We also compared the Av map around ${\lambda}$-Orionis with the optical depth obtained based on the star-count.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.59.2-59.2
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• 2014

Radiative transfer models in a spherical, turbulent interstellar medium (ISM), in which the photon source is situated at the center, are calculated to investigate the correlation between the scattered light and the dust column density. The medium is modeled using fractional Brownian motion structures that are appropriate for turbulent ISM. The correlation plot between the scattered light and optical depth shows substantial scatter and deviation from simple proportionality. It was also found that the overall density contrast is smoothed out in scattered light. In other words, there is an enhancement of the dust-scattered flux in low-density regions, while the scattered flux is suppressed in high-density regions. The correlation becomes less significant as the scattering becomes closer to being isotropic and the medium becomes more turbulent. Therefore, the scattered light observed in near-infrared wavelengths would show much weaker correlation than the observations in optical and ultraviolet wavelengths. We also find that the correlation plot between scattered lights at two different wavelengths shows a tighter correlation than that of the scattered light versus the optical depth.