Characterizing TW Hydra

Sokal, Kimberly R.; Deen, C.; Mace, Gregory N.; Lee, Jae‐Joon; Oh, Hyun-Mee; Kim, Hwi; Kidder, Benjamin; Jaffe, D. T.

doi:10.3847/1538-4357/aaa1e4

Cited by 51 publications

(51 citation statements)

References 46 publications

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“…We cannot rule out that such difference might be explained by the differences in the fitting techniques and the assumptions made in previous studies (Johns-Krull et al 1999). However, due to the increasing amount of evidence showing a dichotomy between optical and NIR temperature measurements (Gully-Santiago et al 2017;Guo et al 2018;Sokal et al 2018), we interpret the temperature difference as due to starspots on the surface of BP Tau. In this scenario, it is reasonable to expect that the IR determination of stellar parameters provides lower temperatures than optical studies, as a large fraction of the flux received in the K band is from the cooler regions in the stellar photosphere.…”

Section: Magnetic Model Verification: Bp Taumentioning

confidence: 85%

“…This means that the effective temperature of BP Tau is likely to be in the range T eff ∼ 4 000 K − 3 600 K. However, we think that neither the optical temperature of ∼ 4 000 K nor the nearinfrared temperature of ∼ 3 600 K truly represent the effective temperature of BP Tau 10 . Examples of this situation have been documented in the literature (Gully-Santiago et al 2017;Sokal et al 2018) and might become even more evident once IR spectroscopic surveys can be performed on a large number of young stars.…”

Section: Magnetic Model Verification: Bp Taumentioning

confidence: 90%

“…We have investigated how the atmospheric stellar parameters change when we use nonmagnetic models to fit the spectrum of YSOs. These types of studies have been performed in the past and the most common outcome is that stellar temperatures change by a few hundred Kelvin, surface gravities vary by up to 0.5 dex, and rotational velocities differ by more than 2 km s −1 (Doppmann & Jaffe 2003;Sokal et al 2018). To set new tests to this long-lasting assumption, we modeled the spectrum of our two YSOs fixing the magnetic field strength to B = 0 kG, and allowing the T eff , log(g), r K , v sin(i), v micro , and CO abundance to vary.…”

Section: Nonmagnetic Models When Estimating Stellar Parameters Of Ysosmentioning

confidence: 99%

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Measuring the Magnetic Field of Young Stars Using iSHELL Observations: BP Tau and V347 Aur

Flores

Reipurth

Boogert

2019

ApJ

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While it has been suggested that there is a connection between the magnetic properties and the internal structure of young stars, there have not been enough magnetic measurements to firmly establish such a correlation at the earliest ages. Here, we contribute to this endeavor by presenting stellar parameters and magnetic field strength measurements of BP Tau and V347 Aur, both stars observed with the near-infrared spectrograph iSHELL. We first test the accuracy of our method by fitting synthetic stellar spectra to a sample of nine main and post-main-sequence stars. We report uncertainties of σ Teff = 91 K in temperature and σ log(g) = 0.14 in gravity. We then apply the modeling technique to BP Tau and measure a surface magnetic field strength of B = 2.5 +0.15 −0.16 kG, confirming literature results. For this star, however, we obtain a much lower temperature value than previous optical studies (∆T ∼ 400 K) and interpret this significant temperature difference as due to the relatively higher impact of starspots at near-infrared wavelengths than at optical wavelengths. We further apply this technique to the class I protostellar source V347 Aur and measure for the first time its magnetic field strength B = 1.36 +0.06 −0.05 kG and its surface gravity log(g) = 3.25 +0.14 −0.14 . Lastly, we combine our measurements with pre-main-sequence stellar evolutionary models and illustrate the effects produced by starspots on the retrieved masses and ages of young stars.

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Section: Magnetic Model Verification: Bp Taumentioning

confidence: 85%

Section: Magnetic Model Verification: Bp Taumentioning

confidence: 90%

Section: Nonmagnetic Models When Estimating Stellar Parameters Of Ysosmentioning

confidence: 99%

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Measuring the Magnetic Field of Young Stars Using iSHELL Observations: BP Tau and V347 Aur

Flores

Reipurth

Boogert

2019

ApJ

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“…In order to identify the mean magnetic field strength of CI Tau, we find the best fit MoogStokes synthetic spectrum compared to the combined IGRINS spectrum of CI Tau. We follow a method similar to that of Sokal et al (2018). First, further processing of the combined spectrum is required to compare to the MoogStokes models.…”

Section: Identifying the Best Fit Synthetic Spectrummentioning

confidence: 99%

The Mean Magnetic Field Strength of CI Tau

Sokal

Johns–Krull

Mace

et al. 2020

ApJ

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We present a blind comparison of two methods to measure the mean surface magnetic field strength of the classical T Tauri star CI Tau based on Zeeman broadening of sensitive spectral lines. Our approach takes advantage of the greater Zeeman broadening at near-infrared compared to optical wavelengths. We analyze a high signal-to-noise, high spectral resolution spectrum from 1.5-2.5µm observed with IGRINS (Immersion GRating INfrared Spectrometer) on the Discovery Channel Telescope. Both stellar parameterization with MoogStokes (which assumes an uniform magnetic field) and modeling with SYNTHMAG (which includes a distribution of magnetic field strengths) yield consistent measurements for the mean magnetic field strength of CI Tau is B of ∼ 2.2 kG. This value is typical compared with measurements for other young T Tauri stars and provides an important contribution to the existing sample given it is the only known developed planetary system hosted by a young classical T Tauri star. Moreover, we potentially identify an interesting and suggestive trend when plotting the effective temperature and the mean magnetic field strength of T Tauri stars. While a larger sample is needed for confirmation, this trend appears only for a subset of the sample, which may have implications regarding the magnetic field generation.

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“…The TW Hydrae Association (TWA) is a nearby ( ∼ 60 pc; Zuckerman & Song 2004;Gaia Collaboration et al (2018)) , young ( ∼ 7-10 Myr; Ducourant et al 2014;Herczeg & Hillenbrand 2015;Sokal et al 2018) group of stars, discovered by Kastner et al (1997). The Young Stellar Objects (YSOs) in TWA differ from the main-sequence stars in Table 1 mainly by differences in log g (∼4.0) and stellar activity.…”

Section: Testing Our Tspec-ldr Scale On Twa Membersmentioning

confidence: 99%

Effective Temperatures of Low-mass Stars from High-resolution H-band Spectroscopy

López-Valdivia

Mace

Sokal

et al. 2019

ApJ

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High-resolution, near-infrared spectra will be the primary tool for finding and characterizing Earthlike planets around low-mass stars. Yet, the properties of exoplanets can not be precisely determined without accurate and precise measurements of the host star. Spectra obtained with the Immersion GRating INfrared Spectrometer (IGRINS) simultaneously provide diagnostics for most stellar parameters, but the first step in any analysis is the determination of the effective temperature. Here we report the calibration of high-resolution H-band spectra to accurately determine effective temperature for stars between 4000-3000 K (∼K8-M5) using absorption line depths of Fe i, OH, and Al i. The field star sample used here contains 254 K and M stars with temperatures derived using BT-Settl synthetic spectra. We use 106 stars with precise temperatures in the literature to calibrate our method with typical errors of about 140 K, and systematic uncertainties less than ∼120 K. For the broadest applicability, we present T eff -line-depth-ratio relationships, which we test on 12 members of the TW Hydrae Association and at spectral resolving powers between ∼10,000-120,000. These ratios offer a simple but accurate measure of effective temperature in cool stars that is distance and reddening independent.

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Characterizing TW Hydra

Cited by 51 publications

References 46 publications

Measuring the Magnetic Field of Young Stars Using iSHELL Observations: BP Tau and V347 Aur

Measuring the Magnetic Field of Young Stars Using iSHELL Observations: BP Tau and V347 Aur

The Mean Magnetic Field Strength of CI Tau

Effective Temperatures of Low-mass Stars from High-resolution H-band Spectroscopy

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