Search for: All records

Understanding the inclinations of stellar spin axes is fundamental for studying planet formation and young binary star evolution. Obliquities between exoplanet orbits and their host stars can be traced to the misalignment of circumstellar disks and stellar rotation. In both single and binary systems, these misalignments can impact disk lifetimes and hinder the formation of planets altogether. Our goal is to derive the inclinations for single and binary systems in the Taurus star-forming region using a unique method that relies on estimates of stellar radii. We first identify rotation periods from TESS and K2 light curves for over a hundred sources. In order to test that these periods reflect the stellar rotation of CTTSs, we model the impact of accretion and other activity on our ability to extract the underlying sinusoidal signal we expect from rotation. We combine these data with projected stellar rotation velocities and effective temperatures derived by fitting a synthetic model grid to IGRINS spectra of our sources. Alongside all of these parameters, we use stellar ages and evolutionary track models from the literature to determine inclination. We present the details of this novel approach and the results from our derived distribution of stellar inclinations. 

Young binary systems offer a unique opportunity to study the fragility of circumstellar disks in dynamically tumultuous environments. In this talk, I will present preliminary ALMA continuum and 12CO emission for several systems, including the puzzling DF Tau. DF Tau is a close visual binary with a semi-major axis of only 14 AU; we find circumstellar disks around both the primary and secondary star. Other disk signatures, i.e. accretion measurements and H-band veiling, indicate only a disk around the primary star. Because the two stars likely formed together, with the same composition, in the same environment, and at the same time, we expect their disks to be co-eval. However the absence of an inner disk around the secondary suggests uneven dissipation. We resolve this contradiction by proposing that the inner disk of DF Tau B is, at minimum, beyond ~0.06 AU and consider several processes which have the potential to accelerate inner disk evolution. 

Abstract In high dispersion spectra of rotating bodies such as stars and planets, the rotation contributes significantly to, and sometimes dominates, the line broadening. We present a simple method for rotationally broadening large wavelength ranges of high-dispersion spectra. The broadening is rapid and scales linearly with the length of the spectrum array. For large wavelength ranges, the method is much faster than the popular convolution-based broadening. We provide the code implementation of this method in a publicly accessible repository. 

Abstract Specifically selected to leverage the unique ultraviolet capabilities of the Hubble Space Telescope, the Hubble Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) is a Director’s Discretionary program of approximately 1000 orbits—the largest ever executed—that produced a UV spectroscopic library of O and B stars in nearby low-metallicity galaxies and accreting low-mass stars in the Milky Way. Observations from ULLYSES combined with archival spectra uniformly sample the fundamental astrophysical parameter space for each mass regime, including spectral type, luminosity class, and metallicity for massive stars, and the mass, age, and disk accretion rate for low-mass stars. The ULLYSES spectral library of massive stars will be critical to characterize how massive stars evolve at different metallicities; to advance our understanding of the production of ionizing photons, and thus of galaxy evolution and the re-ionization of the Universe; and to provide the templates necessary for the synthesis of integrated stellar populations. The massive-star spectra are also transforming our understanding of the interstellar and circumgalactic media of low-metallicity galaxies. On the low-mass end, UV spectra of T Tauri stars contain a plethora of diagnostics of accretion, winds, and the warm disk surface. These diagnostics are crucial for evaluating disk evolution and provide important input to assess atmospheric escape of planets and to interpret powerful probes of disk chemistry, as observed with the Atacama Large Millimeter Array and the James Webb Space Telescope. In this paper, we motivate the design of the program, describe the observing strategy and target selection, and present initial results. 

Abstract The stellar companion to the weak-line T Tauri star DI Tau A was first discovered by the lunar occultation technique in 1989 and was subsequently confirmed by a speckle imaging observation in 1991. It has not been detected since, despite being targeted by five different studies that used a variety of methods and spanned more than 20 yr. Here, we report the serendipitous rediscovery of DI Tau B during our Young Exoplanets Spectroscopic Survey (YESS). Using radial velocity data from YESS spanning 17 yr, new adaptive optics observations from Keck II, and a variety of other data from the literature, we derive a preliminary orbital solution for the system that effectively explains the detection and (almost all of the) non-detection history of DI Tau B. We estimate the dynamical masses of both components, finding that the large mass difference (q∼ 0.17) and long orbital period (≳35 yr) make the DI Tau system a noteworthy and valuable addition to studies of stellar evolution and pre-main-sequence models. With a long orbital period and a small flux ratio (f2/f1) between DI Tau A and B, additional measurements are needed for a better comparison between these observational results and pre-main-sequence models. Finally, we report an average surface magnetic field strength ( $\overline{B}$) for DI Tau A, of ∼0.55 kG, which is unusually low in the context of young active stars. 

Abstract We used the Immersion GRating Infrared Spectrometer (IGRINS) to determine fundamental parameters for 61 K- and M-type young stellar objects (YSOs) located in the Ophiuchus and Upper Scorpius star-forming regions. We employed synthetic spectra and a Markov chain Monte Carlo approach to fit specificK-band spectral regions and determine the photospheric temperature (T), surface gravity ( $\log g$), magnetic field strength (B), projected rotational velocity ( $v\sin i$), andK-band veiling (r_K). We determinedBfor ∼46% of our sample. Stellar parameters were compared to the results from Taurus-Auriga and the TW Hydrae association presented in Paper I of this series. We classified all the YSOs in the IGRINS survey with infrared spectral indices from Two Micron All Sky Survey and Wide-field Infrared Survey Explorer photometry between 2 and 24μm. We found that Class II YSOs typically have lower $\log g$and $v\sin i$, similarB, and higherK-band veiling than their Class III counterparts. Additionally, we determined the stellar parameters for a sample of K and M field stars also observed with IGRINS. We have identified intrinsic similarities and differences at different evolutionary stages with our homogeneous determination of stellar parameters in the IGRINS YSO survey. Considering $\log g$as a proxy for age, we found that the Ophiuchus and Taurus samples have a similar age. We also find that Upper Scorpius and TWA YSOs have similar ages, and are more evolved than Ophiuchus/Taurus YSOs.