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Sokal, Kimberly R.,Deen, Casey P.,Mace, Gregory N.,Lee, Jae-Joon,Oh, Heeyoung,Kim, Hwihyun,Kidder, Benjamin T.,Jaffe, Daniel T. American Astronomical Society 2018 The Astrophysical journal Vol.853 No.2
<P>At 60 pc, TW Hydra (TW Hya) is the closest example of a star with a gas-rich protoplanetary disk, though TW Hya may be relatively old (3-15 Myr). As such, TW Hya is especially appealing for testing our understanding of the interplay between stellar and disk evolution. We present a high-resolution near-infrared spectrum of TW Hya obtained with the Immersion GRating INfrared Spectrometer (IGRINS) to re-evaluate the stellar parameters of TW Hya. We compare these data to synthetic spectra of magnetic stars produced by MoogStokes, and use sensitive spectral line profiles to probe the effective temperature, surface gravity, and magnetic field. A model with T-eff = 3800 K, log g = 4.2, and B = 3.0 kG best fits the near-infrared spectrum of TW Hya. These results correspond to a spectral type of M0.5 and an age of 8 Myr, which is well past the median life of gaseous disks.</P>
Placing the Spotted T Tauri Star LkCa 4 on an HR Diagram
Gully-Santiago, Michael A.,Herczeg, Gregory J.,Czekala, Ian,Somers, Garrett,Grankin, Konstantin,Covey, Kevin R.,Donati, J. F.,Alencar, Silvia H. P.,Hussain, Gaitee A. J.,Shappee, Benjamin J.,Mace, Gre American Astronomical Society 2017 The Astrophysical journal Vol.836 No.2
<P>Ages and masses of young stars are often estimated by comparing their luminosities and effective temperatures to pre-main-sequence stellar evolution tracks, but magnetic fields and starspots complicate both the observations and evolution. To understand their influence, we study the heavily spotted weak-lined T-Tauri star LkCa 4 by searching for spectral signatures of radiation originating from the starspot or starspot groups. We introduce a new methodology for constraining both the starspot filling factor and the spot temperature by fitting two-temperature stellar atmosphere models constructed from PHOENIX synthetic spectra to a high-resolution near-IR IGRINS spectrum. Clearly discernable spectral features arise from both a hot photospheric component T-hot similar to 4100 K and a cool component T-cool similar to 2700-3000 K, which covers similar to 80% of the visible surface. This mix of hot and cool emission is supported by analyses of the spectral energy distribution, rotational modulation of colors and of TiO band strengths, and features in low-resolution optical/near-IR spectroscopy. Although the revised effective temperature and luminosity make. LkCa 4 appear to be. much younger and of much. lower mass than previous estimates from unspotted stellar evolution models, appropriate estimates will require the production and adoption of spotted evolutionary models. Biases from starspots likely afflict most fully convective young stars and contribute to uncertainties in ages and age spreads of open clusters. In some spectral regions, starspots act as a featureless 'veiling' continuum owing to high rotational broadening and heavy line blanketing in cool star spectra. Some evidence is also found for an anticorrelation between the velocities of the warm and cool components.</P>
Auto-guiding Performance from IGRINS Test Observations (Immersion GRating INfrared Spectrograph)
Hye-In Lee,Soojong Pak,Huynh Anh N.Le,Wonseok Kang,Gregory Mace,Michael Pavel,Daniel T.Jaffe,Jae-Joon Lee,Ueejeong Jeong,Michael Pavel,Daniel T.Jaffe,Jae-Joon Lee,Ueejeong Jeong,Moo-Young Chun,Chan Pa 한국천문학회 2014 天文學會報 Vol.39 No.2
THE CHEMICAL COMPOSITIONS OF VERY METAL-POOR STARS HD 122563 AND HD 140283: A VIEW FROM THE INFRARED
Afş,ar, Melike,Sneden, Christopher,Frebel, Anna,Kim, Hwihyun,Mace, Gregory N.,Kaplan, Kyle F.,Lee, Hye-In,Oh, Heeyoung,Oh, Jae Sok,Pak, Soojong,Park, Chan,Pavel, Michael D.,Yuk, In-Soo,Jaffe, Dan American Astronomical Society 2016 The Astrophysical journal Vol.819 No.2
<P>From high resolution (R similar or equal to 45,000), high signal-to-noise ratio (S/N > 400) spectra gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and K photometric bands, we have derived elemental abundances of two bright, well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD 140283. Since these stars have metallicities approaching [Fe/H] = -3, their absorption features are generally very weak. Neutral-species lines of Mg, Si, S and Ca are detectable, as well as those of the light odd-Z elements Na and Al. The derived IR-based abundances agree with those obtained from optical-wavelength spectra. For Mg and Si the abundances from the infrared transitions are improvements to those derived from shorter wavelength data. Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum, from which derived O and C abundances are consistent to those obtained from the traditional [O I] and CH features. IGRINS high resolutions Hand K-band spectroscopy offers promising ways to determine more reliable abundances for additional metal-poor stars whose optical features are either not detectable, or too weak, or are based on lines with analytical difficulties.</P>
Fluorescent H<sub>2</sub>Emission Lines from the Reflection Nebula NGC 7023 Observed with IGRINS
Le, Huynh Anh N.,Pak, Soojong,Kaplan, Kyle,Mace, Gregory,Lee, Sungho,Pavel, Michael,Jeong, Ueejeong,Oh, Heeyoung,Lee, Hye-In,Chun, Moo-Young,Yuk, In-Soo,Pyo, Tae-Soo,Hwang, Narae,Kim, Kang-Min,Park, C American Astronomical Society 2017 The Astrophysical journal Vol.841 No.1
<P>We have analyzed the temperature, velocity, and density of H-2 gas in NGC. 7023 with a high-resolution near-infrared spectrum of the northwestern filament of the reflection nebula. By observing NGC. 7023 in the H and K bands at R similar or equal to 45,000 with the Immersion GRating INfrared Spectrograph, we detected 68 H-2 emission lines within the 1 '' x 15 '' slit. The diagnostic ratio of 2-1 S(1)/1-0 S(1) is 0.41-0.56. In addition, the estimated ortho-to-para ratio (OPR) is 1.63-1.82, indicating that the H-2 emission transitions in the observed region arise mostly from gas excited by UV fluorescence. Gradients in the temperature, velocity, and OPR within the observed area imply motion of the photodissociation region (PDR) relative to the molecular cloud. In addition, we derive the column density of H-2 from the observed emission lines and compare these results with PDR models in the literature covering a range of densities and incident UV field intensities. The notable difference between PDR model predictions and the observed data, in high rotational J levels of v = 1, is that the predicted formation temperature for newly formed H-2 should be lower than that of the model predictions. To investigate the density distribution, we combine pixels in 1 '' x 1 '' areas and derive the density distribution at the 0.002 pc scale. The derived gradient of density suggests that NGC 7023 has a clumpy structure, including a high clump density of similar to 10(5) cm(-3) with a size smaller than similar to 5 x 10(- 3) pc embedded in lower-density regions of 10(3)-10(4) cm(-3).</P>
Kaplan, Kyle F.,Dinerstein, Harriet L.,Oh, Heeyoung,Mace, Gregory N.,Kim, Hwihyun,Sokal, Kimberly R.,Pavel, Michael D.,Lee, Sungho,Pak, Soojong,Park, Chan,Oh, Jae Sok,Jaffe, Daniel T. American Astronomical Society 2017 The Astrophysical journal Vol.838 No.2
<P>We present a deep near-infrared spectrum of the Orion Bar Photodissociation Region (PDR) taken with the Immersion Grating INfrared Spectrometer (IGRINS) on the 2.7 m telescope at the McDonald Observatory. IGRINS has high spectral resolution (R similar to 45,000) and instantaneous broad wavelength coverage (1.45-2.45 mu m), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H-2) that arise from transitions out of 69 upper rovibration levels of the electronic ground state. These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H2 and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments (T = 50-250 K, n(H) = 10(5)-10(7) cm(-3)) embedded in a warmer lower density medium (T = 250-1000 K, n(H) = 10(4)-10(5) cm(-3)). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H2 level populations well, to constrain the temperature to a range of 600-650. K and the density to n(H) = 2.5 x 10(3) -10(4) cm(-3). The best-fit model gives T = 625 K and n(H) = 5 x 10(3) cm(-3). This well-constrained warm temperature is consistent with kinetic temperatures found by other studies for the Orion Bar's lower density medium. However, the range of densities well fit by the model grid is marginally lower than those reported by other studies. We could be observing lower density gas than the surrounding medium, or perhaps a density-sensitive parameter in our models is not properly estimated.</P>
IGRINS SPECTROSCOPY OF CLASS I SOURCES: IRAS 03445+3242 AND IRAS 04239+2436
Lee, Seokho,Lee, Jeong-Eun,Park, Sunkyung,Lee, Jae-Joon,Kidder, Benjamin,Mace, Gregory N.,Jaffe, Daniel T. American Astronomical Society 2016 The Astrophysical journal Vol.826 No.2
<P>We have detected molecular and atomic line emission from the hot and warm disks of two Class I sources, IRAS 03445+3242 and IRAS 04239+2436, using the high-resolution Immersion GRating INfrared Spectrograph (IGRINS). CO overtone band transitions and near-IR lines of Na I and Ca I, all in emission, trace the hot inner disk, while CO rovibrational absorption spectra of the first overtone transition trace the warm gas within the inner few AU of the disk. The emission-line profiles for both sources show evidence for Keplerian disks. A thin Keplerian disk with power-law temperature and column density profiles with a projected rotational velocity of similar to 60-75 km s(-1) and a gas temperature of similar to 3500 K at the innermost annulus can reproduce the CO overtone band emission. Na I and Ca I emission lines also arise from this disk, but they show complicated line features possibly affected by photospheric absorption lines. Multi-epoch observations show asymmetric variations of the line profiles on one-year (CO overtone bandhead and atomic lines for IRAS 03445+3242) or on one-day (atomic lines for IRAS 04239+2436) timescales, implying non-axisymmetric features in disks. The narrow CO rovibrational absorption spectra (v = 0 -> 2) indicate that both warm (>150 K) and cold (similar to 20-30 K) CO gas are present along the line of sight to the inner disk. This study demonstrates the power of IGRINS as a tool for studies of the sub-AU-scale hot and AU-scale warm protoplanetary disks with its simultaneous coverage of the full H and K bands with high spectral resolution (R = 45,000) allowing many aspects of the sources to be investigated at once.</P>