Search

Radially extended disk winds could be the key to unlocking how protoplanetary disks accrete and how planets form and migrate. A distinctive characteristic is their nested morphology of velocity and chemistry. Here we report JWST/NIRSpec spectro-imaging of four young stars with edge-on disks in the Taurus star-forming region that demonstrate the ubiquity of this structure. In each source, a fast collimated jet traced by [Fe II] is nested inside a hollow cavity within wider lower-velocity H2 and, in one case, also CO ro-vibrational (v=1-0) emission. Furthermore, in one of our sources, ALMA CO(2-1) emission, paired with our NIRSpec images, reveals the nested wind structure extends further outward. This nested wind morphology strongly supports theoretical predictions for wind-driven accretion and underscores the need for theoretical work to assess the role of winds in the formation and evolution of planetary systems, Comment: This preprint has not undergone peer review or any post-submission improvements or corrections. The Version of Record of this article is published in Nature Astronomy and is available online at https://doi.org/10.1038/s41550-024-02385-7

Accretion plays a central role in the physics that governs the evolution and dispersal of protoplanetary disks. The primary goal of this paper is to analyze the stability over time of the mass accretion rate onto TW Hya, the nearest accreting solar-mass young star. We measure veiling across the optical spectrum in 1169 archival high-resolution spectra of TW Hya, obtained from 1998--2022. The veiling is then converted to accretion rate using 26 flux-calibrated spectra that cover the Balmer jump. The accretion rate measured from the excess continuum has an average of $2.51\times10^{-9}$~M$_\odot$~yr$^{-1}$ and a Gaussian distribution with a FWHM of 0.22 dex. This accretion rate may be underestimated by a factor of up to 1.5 because of uncertainty in the bolometric correction and another factor of 1.7 because of excluding the fraction of accretion energy that escapes in lines, especially Ly$\alpha$. The accretion luminosities are well correlated with He line luminosities but poorly correlated with H$\alpha$ and H$\beta$ luminosity. The accretion rate is always flickering over hours but on longer timescales has been stable over 25 years. This level of variability is consistent with previous measurements for most, but not all, accreting young stars., Comment: Accepted by ApJ. 31 pages

The detection of emission lines associated with accretion processes is a direct method for studying how and where gas giant planets form, how young planets interact with their natal protoplanetary disk and how volatile delivery to their atmosphere takes place. H$\alpha$ ($\lambda=0.656\,\mu$m) is expected to be the strongest accretion line observable from the ground with adaptive optics systems, and is therefore the target of specific high-contrast imaging campaigns. We present MagAO-X and HST data obtained to search for H$\alpha$ emission from the previously detected protoplanet candidate orbiting AS209, identified through ALMA observations. No signal was detected at the location of the candidate, and we provide limits on its accretion. Our data would have detected an H$\alpha$ emission with $F_\mathrm{H\alpha}>2.5\pm0.3 \times10^{-16}$ erg s$^{-1}$ cm$^{-2}$, a factor 6.5 lower than the HST flux measured for PDS70b (Zhou et al., 2021). The flux limit indicates that if the protoplanet is currently accreting it is likely that local extinction from circumstellar and circumplanetary material strongly attenuates its emission at optical wavelengths. In addition, the data reveal the first image of the jet north of the star as expected from previous detections of forbidden lines. Finally, this work demonstrates that current ground-based observations with extreme adaptive optics systems can be more sensitive than space-based observations, paving the way to the hunt for small planets in reflected light with extremely large telescopes., Comment: 13 pages, 5 figures, accepted for publication in AJ

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. Here, we analyze high-resolution ($\Delta v \sim$ 7 kms$^{-1}$) optical spectra from a sample of 115 T Tauri stars in the $\sim 5-10$ Myr Upper Sco association and focus on the [O I]$\lambda$6300 and H$\alpha$ lines to trace disk winds and accretion, respectively. Our sample covers a large range in spectral type and we divide it into Warm (G0-M3) and Cool (later than M3) to facilitate comparison with younger regions. We detect the [O I]$\lambda$6300 line in 45 out of 87 upper sco sources with protoplanetary disks and 32 out of 45 are accreting based on H$\alpha$ profiles and equivalent widths. All [O I] $\lambda$6300 Upper Sco profiles have a low-velocity (centroid $< -30$ kms$^{-1}$, LVC) emission and most (36/45) can be fit by a single Gaussian (SC). The SC distribution of centroid velocities and FWHMs is consistent with MHD disk winds. We also find that the Upper Sco sample follows the same accretion luminosity$-$LVC [O I]$\lambda$6300 luminosity relation and the same anti-correlation between SC FWHM and WISE W3-W4 spectral index as the younger samples. These results indicate that accretion and disk winds coevolve and that, as inner disks clear out, wind emission arises further away from the star. Finally, our large spectral range coverage reveals that Cool stars have larger FWHMs normalized by stellar mass than Warm stars indicating that [O I]$\lambda$6300 emission arises closer in towards lower mass/lower luminosity stars., Comment: 47 pages, 32 figures; ApJ accepted

The assembly and architecture of planetary systems strongly depend on the physical processes governing the evolution and dispersal of protoplanetary disks. Since Protostars and Planets VI, new observations and theoretical insights favor disk winds as being one of those key processes. This chapter provides a comprehensive review of recent observations probing outflowing gas launched over a range of disk radii for a wide range of evolutionary stages, enabling an empirical understanding of how winds evolve. In parallel, we review theoretical advancements in both magnetohydrodynamic and photoevaporative disk wind models and identify predictions that can be confronted with observations. By linking theory and observations we critically assess the role of disk winds in the evolution and dispersal of protoplanetary disks. Finally, we explore the impact of disk winds on planet formation and evolution and highlight theoretical work, observations, and critical tests for future progress., Comment: Review chapter to appear in Protostars and Planets VII, Editors: Shu-ichiro Inutsuka, Yuri Aikawa, Takayuki Muto, Kengo Tomida, and Motohide Tamura

The Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) Director's Discretionary Program of low-mass pre-main-sequence stars, coupled with forthcoming data from ALMA and JWST, will provide the foundation to revolutionize our understanding of the relationship between young stars and their protoplanetary disks. A comprehensive evaluation of the physics of disk evolution and planet formation requires understanding the intricate relationships between mass accretion, mass outflow, and disk structure. Here we describe the Outflows and Disks around Young Stars: Synergies for the Exploration of ULLYSES Spectra (ODYSSEUS) Survey and present initial results of the classical T Tauri Star CVSO 109 in Orion OB1b as a demonstration of the science that will result from the survey. ODYSSEUS will analyze the ULLYSES spectral database, ensuring a uniform and systematic approach in order to (1) measure how the accretion flow depends on the accretion rate and magnetic structures, (2) determine where winds and jets are launched and how mass-loss rates compare with accretion, and (3) establish the influence of FUV radiation on the chemistry of the warm inner regions of planet-forming disks. ODYSSEUS will also acquire and provide contemporaneous observations at X-ray, optical, NIR, and millimeter wavelengths to enhance the impact of the ULLYSES data. Our goal is to provide a consistent framework to accurately measure the level and evolution of mass accretion in protoplanetary disks, the properties and magnitudes of inner-disk mass loss, and the influence of UV radiation fields that determine ionization levels and drive disk chemistry., Comment: accepted to ApJ

We used high-resolution near-infrared spectroscopy from the NIRSPEC instrument on the Keck II telescope, taken over multiple epochs spanning five years, to examine two young binary T Tauri star systems, S Corona Australis and VV Corona Australis. The stars in these 1-2" separation systems have optically thick circumstellar disks and high extinctions at optical and near-infrared wavelengths. Using a combination of new and archival data, we have determined the spectral types of all the stars in these two systems for the first time, examined the variable NIR veiling, measured the emission line equivalent widths, and created spectral energy distributions. They have similar spectral types (K7-M1) and are at approximately the same evolutionary stage, allowing comparison of the four stars in the two systems. We conclude that S CrA and VV CrA are young binary systems of stars bridging the Class I and Class II evolutionary stages, characterized by high accretion luminosities and variable emission lines., Comment: 16 pages, accepted to The Astrophysical Journal

We present a high-resolution ($\sim0.''12$, $\sim16$ au, mean sensitivity of $50~\mu$Jy~beam$^{-1}$ at 225 GHz) snapshot survey of 32 protoplanetary disks around young stars with spectral type earlier than M3 in the Taurus star-forming region using Atacama Large Millimeter Array (ALMA). This sample includes most mid-infrared excess members that were not previously imaged at high spatial resolution, excluding close binaries and highly extincted objects, thereby providing a more representative look at disk properties at 1--2 Myr. Our 1.3 mm continuum maps reveal 12 disks with prominent dust gaps and rings, 2 of which are around primary stars in wide binaries, and 20 disks with no resolved features at the observed resolution (hereafter smooth disks), 8 of which are around the primary star in wide binaries. The smooth disks were classified based on their lack of resolved substructures, but their most prominent property is that they are all compact with small effective emission radii ($R_{\rm eff,95\%} \lesssim 50$ au). In contrast, all disks with $R_{\rm eff,95\%}$ of at least 55 au in our sample show detectable substructures. Nevertheless, their inner emission cores (inside the resolved gaps) have similar peak brightness, power law profiles, and transition radii to the compact smooth disks, so the primary difference between these two categories is the lack of outer substructures in the latter. These compact disks may lose their outer disk through fast radial drift without dust trapping, or they might be born with small sizes. The compact dust disks, as well as the inner disk cores of extended ring disks, that look smooth at the current resolution will likely show small-scale or low-contrast substructures at higher resolution. The correlation between disk size and disk luminosity correlation demonstrates that some of the compact disks are optically thick at millimeter wavelengths., Comment: ApJ accepted, 25 pages, 11 figures

KH 15D is a well-known spectroscopic binary because of its unique and dramatic photometric variability. The variability is explained by a circumbinary dust ring but the ring itself was never directly detected. We present a new interpretation of the double-peaked [O~{\scriptsize I}]\,$\lambda$6300 profiles as originating from the hot disk surface of KH 15D. By modeling these profiles, we measure emitting radii between $\sim$0.5--5 au, basically a gaseous ring very similar in radial extent to the dust ring inferred from modeling the system's photometric variability. We also discuss the possibility that external photoevaporation driven by UV photons from the nearby massive star HD~47887 has truncated the outer edge of the disk to the observed value., Comment: 8 pages, 5 figures, accepted by ApJL

We present a survey of optical [OI] emission at 6300 \AA\ toward 65 TTauri stars at the spectral resolution of $\sim7$ km/s. Past work identified a highly blueshifted velocity component (HVC) tracing microjets, and a less blueshifted low-velocity-component (LVC) attributed to winds. We focus here on the LVC kinematics to investigate links between winds, jets, accretion, and disk dispersal. We track the behavior of four types of LVC components: a broad and narrow component ("BC" and "NC") in LVCs that are decomposed into two Gaussians, which typically have an HVC, and the single-Gaussian LVC profiles separated into those that have an HVC ("SCJ") and those that do not ("SC"). LVC centroid velocities and line widths correlate with HVC equivalent width and accretion luminosity, suggesting that LVC/winds and HVC/jets are kinematically linked and connected to accretion. The deprojected HVC velocity correlates with accretion luminosity, showing that faster jets come with higher accretion. BC and NC kinematics correlate and their blueshifts are maximum at $\sim 35^{\circ}$, suggesting a conical wind geometry with this semi-opening angle. Only SCs include $n_{13-31}$ up to $\sim3$ and their properties correlate with this infrared index, showing that [OI] emission recedes to larger radii as the inner dust is depleted, tracing less dense/hot gas and a decrease in wind velocity. All together, these findings support a scenario where optically thick, accreting inner disks launch radially-extended MHD disk winds that feed jets, and where inner disk winds recede to larger radii and jets disappear in concert with dust depletion., Comment: Accepted for publication on ApJ

Rings are the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution ($\sim0.12''$) ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of sub-mm brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns and high contrast azimuthal asymmetries are not detected. Fits of disk models to the visibilities lead to estimates of the location and shape of gaps and rings, the flux in each disk component, and the size of the disk. The dust substructures occur across a wide range of stellar mass and disk brightness. Disks with multiple rings tend to be more massive and more extended. The correlation between gap locations and widths, the intensity contrast between rings and gaps, and the separations of rings and gaps could all be explained if most gaps are opened by low-mass planets (super-Earths and Neptunes) in the condition of low disk turbulence ($\alpha=10^{-4}$). The gap locations are not well correlated with the expected locations of CO and N$_2$ ice lines, so condensation fronts are unlikely to be a universal mechanism to create gaps and rings, though they may play a role in some cases., Comment: 23 pages, 11 figures, ApJ accepted

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. We report the first high-resolution ($\Delta v\sim$6\kms) analysis of [S II] $\lambda$4068, [O I] $\lambda$5577, and [O I] $\lambda$6300 lines from a sample of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into three kinematic components: a high-velocity component (HVC) associated with jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We confirm previous findings that many LVCs are blueshifted by more than 1.5 kms$^{-1}$ thus most likely trace a slow disk wind. We further show that the profiles of individual components are similar in the three lines. We find that most LVC-BC and NC line ratios are explained by thermally excited gas with temperatures between 5,000$-$10,000 K and electron densities $\sim10^{7}-10^{8}$ cm$^{-3}$. The HVC ratios are better reproduced by shock models with a pre-shock H number density of $\sim10^{6}-10^{7}$ cm$^{-3}$. Using these physical properties, we estimate $\dot{M}_{\rm wind}/\dot{M}_{\rm acc}$ for the LVC and $\dot{M}_{\rm jet}/\dot{M}_{\rm acc}$ for the HVC. In agreement with previous work, the mass carried out in jets is modest compared to the accretion rate. With the likely assumption that the NC wind height is larger than the BC, the LVC-BC $\dot{M}_{\rm wind}/\dot{M}_{\rm acc}$ is found to be higher than the LVC-NC. These results suggest that most of the mass loss occurs close to the central star, within a few au, through an MHD driven wind. Depending on the wind height, MHD winds might play a major role in the evolution of the disk mass., Comment: 45 pages, 23 figures, and 7 tables, accepted by ApJ

Interstellar reddening corrections are necessary to reconstruct the intrinsic spectral energy distributions (SEDs) of accreting protostellar systems. The stellar SED determines the heating and chemical processes that can occur in circumstellar disks. Measurement of neutral hydrogen absorption against broad Lyman-$\alpha$ emission profiles in young stars can be used to obtain the total H I column density (N(H I)) along the line of sight. We measure N(H I) with new and archival ultraviolet observations from the Hubble Space Telescope ($HST$) of 31 classical T Tauri and Herbig Ae/Be stars. The H I column densities range from log$_{10}$(N(H I)) $\approx 19.6 - 21.1$, with corresponding visual extinctions of A$_{V}$ $= 0.02 - 0.72$ mag, assuming an R$_{V}$ of 3.1. We find that the majority of the H I absorption along the line of sight likely comes from interstellar rather than circumstellar material. Extinctions derived from new $HST$ blue-optical spectral analyses, previous IR and optical measurements, and new X-ray column densities on average overestimate the interstellar extinction toward young stars compared to the N(H I) values by $\sim 0.6$ mag. We discuss possible explanations for this discrepancy in the context of a protoplanetary disk geometry., Comment: 20 pages, 10 figures

In accreting young stars one of the prominent spectral features in the near infrared is the Paschen and Brackett series in emission. We examine hydrogen line ratios for 16 classical T Tauri stars from SpeX spectra and and assess the trends with veiling and accretion. The observed line ratios are compared to two theoretical models for line formation: (1) Baker and Menzel's (1938) Case B for radiative ionization and recombination and (2) a set of local line excitation calculations designed to replicate the conditions in T Tauri winds and magnetic accretion columns (Kwan & Fischer 2011). While the comparison between Case B and observed line ratios implies a wide range in electron density and temperature among the hydrogen line formation regions in T Tauri stars, the predictions of the local line excitation models give consistent results across multiple diagnostics. Under the assumptions of the local line excitation calculations, we find that n_H in the hydrogen line formation region is constrained to 2x10^10 -- 2x10^11 cm^-3, where stars with higher accretion rates have densities at the higher end of this range. Because of uncertainties in extinction, temperature is not well delineated but falls within the range expected for collisional excitation to produce the line photons. We introduce new diagnostics for assessing extinction based on near infrared hydrogen line ratios from the local line excitation calculations., Comment: Accepted by ApJ, 17 pages, 13 figures; v2 has some minor copyediting

The formation time, masses, and location of planets are strongly impacted by the physical mechanisms that disperse protoplanetary disks and the timescale over which protoplanetary material is cleared out. Accretion of matter onto the central star, protostellar winds/jets, magnetic disk winds, and photoevaporative winds operate concurrently. Hence, disentangling their relative contribution to disk dispersal requires identifying diagnostics that trace different star-disk environments. Here, we analyze the low velocity component (LVC) of the Oxygen optical forbidden lines, which is found to be blueshifted by a few km/s with respect to the stellar velocity. We find that the [OI] LVC profiles are different from those of [NeII] at 12.81\mu m and CO at 4.7\mu m lines pointing to different origins for these gas lines. We report a correlation between the luminosity of the [OI] LVC and the accretion luminosity Lacc. We do not find any correlation with the X-ray luminosity, while we find that the higher is the stellar FUV luminosity, the higher is the luminosity of the [OI] LVC. In addition, we show that the [OI]6300\AA/5577\AA\ ratio is low (ranging between 1 and 8). These findings favor an origin of the [OI] LVC in a region where OH is photodissociated by stellar FUV photons and argue against thermal emission from an X-ray-heated layer. Detailed modeling of two spectra with the highest S/N and resolution shows that there are two components within the LVC: a broad, centrally peaked component that can be attributed to gas arising in a warm disk surface in Keplerian rotation (with FWHM between ~40 and ~60 km/s), and a narrow component (with FWHM ~10 km/s and small blueshifts of ~2 km/s) that may arise in a cool (<1,000 K) molecular wind., Comment: 16 pages, 10 figures

For Classical T Tauri Stars (CTTSs), the resonance lines of N V, Si IV, and C IV, as well as the He II 1640 A line, act as diagnostics of the accretion process. Here we assemble a large high-resolution dataset of these lines in CTTSs and Weak T Tauri Stars (WTTSs). We present data for 35 stars: one Herbig Ae star, 28 CTTSs, and 6 WTTSs. We decompose the C IV and He II lines into broad and narrow Gaussian components (BC & NC). The most common (50 %) C IV line morphology in CTTSs is that of a low-velocity NC together with a redshifted BC. The velocity centroids of the BCs and NCs are such that V_BC > 4 * V_NC, consistent with the predictions of the accretion shock model, in at most 12 out of 22 CTTSs. We do not find evidence of the post-shock becoming buried in the stellar photosphere due to the pressure of the accretion flow. The He II CTTSs lines are generally symmetric and narrow, less redshifted than the CTTSs C IV lines, by ~10 km/sec. The flux in the BC of the He II line is small compared to that of the C IV line, consistent with models of the pre-shock column emission. The observations are consistent with the presence of multiple accretion columns with different densities or with accretion models that predict a slow-moving, low-density region in the periphery of the accretion column. For HN Tau A and RW Aur A, most of the C IV line is blueshifted suggesting that the C IV emission is produced by shocks within outflow jets. In our sample, the Herbig Ae star DX Cha is the only object for which we find a P-Cygni profile in the C IV line, which argues for the presence of a hot (10^5 K) wind. For the overall sample, the Si IV and N V line luminosities are correlated with the C IV line luminosities, although the relationship between Si IV and C IV shows large scatter about a linear relationship and suggests that TW Hya, V4046 Sgr, AA Tau, DF Tau, GM Aur, and V1190 Sco are silicon-poor., Comment: Accepted in the ApJSS. 52 pages, 9 tables, 20 figures

We analyze the accretion properties of 21 low mass T Tauri stars using a dataset of contemporaneous near ultraviolet (NUV) through optical observations obtained with the Hubble Space Telescope Imaging Spectrograph (STIS) and the ground based Small and Medium Aperture Research Telescope System (SMARTS), a unique dataset because of the nearly simultaneous broad wavelength coverage. Our dataset includes accreting T Tauri stars (CTTS) in Taurus, Chamaeleon I, $\eta$ Chamaeleon and the TW Hydra Association. For each source we calculate the accretion rate by fitting the NUV and optical excesses above the photosphere, produced in the accretion shock, introducing multiple accretion components characterized by a range in energy flux (or density) for the first time. This treatment is motivated by models of the magnetospheric geometry and accretion footprints, which predict that high density, low filling factor accretion spots co-exist with low density, high filling factor spots. By fitting the UV and optical spectra with multiple accretion components, we can explain excesses which have been observed in the near infrared. Comparing our estimates of the accretion rate to previous estimates, we find some discrepancies; however, they may be accounted for when considering assumptions for the amount of extinction and variability in optical spectra. Therefore, we confirm many previous estimates of the accretion rate. Finally, we measure emission line luminosities from the same spectra used for the accretion rate estimates, to produce correlations between accretion indicators (H$\beta$, Ca II K, C II] and Mg II) and accretion properties obtained simultaneously., Comment: 47 pages, 16 figures, accepted for publication in ApJ

Young stars surrounded by disks with very low mass accretion rates are likely in the final stages of inner disk evolution and therefore particularly interesting to study. We present ultraviolet (UV) observations of the ~5-9 Myr old stars RECX-1 and RECX-11, obtained with the Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), as well as optical and near infrared spectroscopic observations. The two stars have similar levels of near UV emission, although spectroscopic evidence indicates that RECX-11 is accreting and RECX-1 is not. The line profiles of Halpha and He I 10830 in RECX-11 show both broad and narrow redshifted absorption components that vary with time, revealing the complexity of the accretion flows. We show that accretion indicators commonly used to measure mass accretion rates, e.g. U band excess luminosity or the Ca II triplet line luminosity are unreliable for low accretors, at least in the middle K spectral range. Using RECX-1 as a template for the intrinsic level of photospheric and chromospheric emission, we determine an upper limit of 3 x 10^-10 solar masses/ year for RECX-11. At this low accretion rate, recent photoevaporation models predict that an inner hole should have developed in the disk. However, the spectral energy distribution of RECX-11 shows fluxes comparable to the median of Taurus in the near infrared, indicating that substantial dust remains. Fluorescent H_2 emission lines formed in the innermost disk are observed in RECX-11, showing that gas is present in the inner disk, along with the dust., Comment: 30 pages, 9 figures, Accepted to ApJ

We present the first characterization of the excess continuum emission of accreting T Tauri stars between optical and near-infrared wavelengths. With nearly simultaneous spectra from 0.48 to 2.4 microns acquired with HIRES and NIRSPEC on Keck and SpeX on the IRTF, we find significant excess continuum emission throughout this region, including the I, Y, and J bands, which are usually thought to diagnose primarily photospheric emission. The IYJ excess correlates with the excess in the V band, attributed to accretion shocks in the photosphere, and the excess in the K band, attributed to dust in the inner disk near the dust sublimation radius, but it is too large to be an extension of the excess from these sources. The spectrum of the excess emission is broad and featureless, suggestive of blackbody radiation with a temperature between 2200 and 5000 K. The luminosity of the IYJ excess is comparable to the accretion luminosity inferred from modeling the blue and ultraviolet excess emission and may require reassessment of disk accretion rates. The source of the IYJ excess is unclear. In stars of low accretion rate, the size of the emitting region is consistent with cooler material surrounding small hot accretion spots in the photosphere. However, for stars with high accretion rates, the projected area is comparable to or exceeds that of the stellar surface. We suggest that at least some of the IYJ excess emission arises in the dust-free gas inside the dust sublimation radius in the disk., Comment: Accepted to ApJ, 31 pages, 21 figures

We take advantage of good atmospheric transparency and the availability of high quality instrumentation in the 1 um near-infrared atmospheric window to present a grid of F, G, K, and M spectral standards observed at high spectral resolution (R ~ 25,000). In addition to a spectral atlas, we present a catalog of atomic line absorption features in the 0.95-1.11 um range. The catalog includes a wide range of line excitation potentials, from 0-13 eV, arising from neutral and singly ionized species, most frequently those of Fe I and Ti I at low excitation, Cr I, Fe I, and Si I at moderate excitation, and C I, S I, and Si I having relatively high excitation. The spectra also include several prominent molecular bands from CN and FeH. For the atomic species, we analyze trends in the excitation potential, line depth, and equivalent width across the grid of spectroscopic standards to identify temperature and surface gravity diagnostics near 1 um. We identify the line ratios that appear especially useful for spectral typing as those involving Ti I and C I or S I, which are temperature sensitive in opposite directions, and Sr II, which is gravity sensitive at all spectral types. Ascii versions of all spectra are available to download with the electronic version of the journal., Comment: 40 pages, 21 figures, 4 tables, spectra available for download with source file, updated to mirror published version

Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star-disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin-up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer a unique opportunity to study the connection between accretion and winds and their relation to stellar spindown. Although spectroscopic indicators of high velocity T Tauri winds have been known for decades, the line of He I 10830 offers a promising new diagnostic to probe the magnetically controlled star-disk interaction and wind-launching region. The high opacity and resonance scattering properties of this line offer a powerful probe of the geometry of both the funnel flow and the inner wind that, together with other atomic and molecular spectral lines covering a wide range of excitation and ionization states, suggests that the magnetic interaction between the star and disk, and the subsequent launching of the inner high velocity wind, is sensitive to the disk accretion rate., Comment: invited review to appear in Proceedings of the 15th Workshop of Cool Stars, Stellar Systems, and the Sun (2008)

We probe the geometry of magnetospheric accretion in classical T Tauri stars by modeling red absorption at He I 10830 via scattering of the stellar and veiling continua. Under the assumptions that the accretion flow is an azimuthally symmetric dipole and helium is sufficiently optically thick that all incident 1-micron radiation is scattered, we illustrate the sensitivity of He I 10830 red absorption to both the size of the magnetosphere and the filling factor of the hot accretion shock. We compare model profiles to those observed in 21 CTTS with subcontinuum redshifted absorption at He I 10830 and find that about half of the stars have red absorptions and 1-micron veilings that are consistent with dipole flows of moderate width with accretion shock filling factors matching the size of the magnetospheric footpoints. However, the remaining 50% of the profiles, with a combination of broad, deep absorption and low 1-micron veiling, require very wide flows where magnetic footpoints are distributed over 10-20% of the stellar surface but accretion shock filling factors are < 1%. We model these profiles by invoking large magnetospheres dilutely filled with accreting gas, leaving the disk over a range of radii in many narrow "streamlets" that fill only a small fraction of the entire infall region. In some cases accreting streamlets need to originate in the disk between several stellar radii and at least the corotation radius. A few stars have such deep absorption at velocities greater than half the stellar escape velocity that flows near the star with less curvature than a dipole trajectory seem to be required., Comment: 26 pages, emulateapj format, Accepted by ApJ, to appear 2008 November 10

The high opacity of He I 10830 makes it an exceptionally sensitive probe of the inner wind geometry of accreting T Tauri stars. In this line blueshifted absorption below the continuum results from simple scattering of stellar photons, a situation which is readily modeled without definite knowledge of the physical conditions and recourse to multi-level radiative transfer. We present theoretical line profiles for scattering in two possible wind geometries, a disk wind and a wind emerging radially from the star, and compare them to observed He I 10830 profiles from a survey of classical T Tauri stars. The comparison indicates that subcontinuum blueshifted absorption is characteristic of disk winds in ~30% of the stars and of stellar winds in ~40%. We further conclude that for many stars the emission profile of helium likely arises in stellar winds, increasing the fraction of accreting stars inferred to have accretion-powered stellar winds to ~60%. Stars with the highest disk accretion rates are more likely to have stellar wind than disk wind signatures and less likely to have redshifted absorption from magnetospheric funnel flows. This suggests the possibility that when accretion rates are high, disks can extend closer to the star, magnetospheric accretion zones can be reduced in size and conditions arise that favor radially outflowing stellar winds., Comment: 41 pages, 11 figures. Accepted by Astrophysical Journal

In a high dispersion 1 micron survey of 39 classical T Tauri stars veiling is detected in 80%, and He I 10830 and Pgamma line emission in 97% of the stars. On average, the 1 micron veiling exceeds the level expected from previously identified sources of excess emission, suggesting the presence of an additional contributor to accretion luminosity in the star-disk interface region. Strengths of both lines correlate with veiling, and at Pgamma there is a systematic progression in profile morphology with veiling. He I 10830 has an unprecedented sensitivity to inner winds, showing blueshifted absorption below the continuum in 71% of the CTTS compared to 0% at pgamma. This line is also sensitive to magnetospheric accretion flows, with redshifted absorption below the continuum found in 47% of the CTTS compared to 24% at Pgamma. The blueshifted absorption at 10830 shows considerable diversity in its breadth and penetration depth into the continuum, indicating that a range of inner wind conditions exist in accreting stars. We interpret the broadest and deepest blue absorptions as formed from scattering of the 1 micron continuum by outflowing gas whose full acceleration region envelopes the star, suggesting radial outflow from the star. In contrast, narrow blue absorption with a range of radial velocities more likely arises via scattering of the 1 micron continuum by a wind emerging from the inner disk. Both stellar and disk winds are accretion powered since neither is seen in non-accreting WTTS and among the CTTS helium strength correlates with veiling., Comment: 55 pages, including 16 figures. Astrophysical Journal, accepted

We present a catalog of J-band spectra for 88 fundamental MK standard stars observed at a resolving power of R ~ 3000. This contribution serves as a companion atlas to the K-band spectra published by Wallace and Hinkle (1997) and the H-band atlas of Meyer et al. (1998). We report data from 7400-9550 1/cm (1.05-1.34 microns) for stars of spectral types O7-M6 and luminosity classes I-V as defined in the MK system. In reducing these data, special care has been taken to remove time-variable telluric features of water vapor. We identify atomic and molecular indices which are both temperature and luminosity sensitive that aid in the classification of stellar spectra in the J-band. In addition to being useful in the classification of late-type stars, the J-band contains several features of interest in the study of early-type stellar photospheres. These data are available electronically for anonymous FTP in addition to being served on the World Wide Web., Comment: Accepted for publication in the Astrophysical Journal. 17 pages including 4 tables, 10 figures in PNG format. Complete PostScript version at http://gould.as.arizona.edu/mmeyer data at http://www.noao.edu/archives.html

We present a catalogue of H-band spectra for 85 stars of approximately solar abundance observed at a resolving power of 3000 with the KPNO Mayall 4m FTS. The atlas covers spectral types O7-M5 and luminosity classes I-V as defined on the MK system. We identify both atomic and molecular indices and line-ratios which are temperature and luminosity sensitive allowing spectral classification to be carried out in the H-band. The line ratios permit spectral classification in the presence of continuum excess emission, which is commonly found in pre-main sequence and evolved stars. We demonstrate that with spectra of R = 1000 obtained at SNR > 50 it is possible to derive spectral types within +- 2 subclasses for late-type stars. These data are available electronically through the Astronomical Data Center in addition to being served on the World-Wide-Web., Comment: To appear in the November 20, 1998 issue of ApJ (Volume 508, #1)