The far-UV spectrum of T Tauri stars -- I. The relevance of the IUE Newly Extracted Spectra (original) (raw)
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Observations of T Tauri Stars usingHubble Space TelescopeGHRS. I. Far‐Ultraviolet Emission Lines
The Astrophysical Journal, 2002
We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists of spectral ranges 40Å wide centered on 1345, 1400, 1497, 1550, and 1900Å. These UV spectra show strong Si IV, and C IV emission, and large quantities of sharp (∼ 40 km s −1) H 2 lines. All the H 2 lines belong to the Lyman band and all the observed lines are single peaked and optically thin. The averages of all the H 2 lines centroids for each star are negative which may indicate that they come from an outflow. We interpret the emission in H 2 as being due to fluorescence, mostly by H Lyα and identify seven excitation routes within 4Å of that line. We obtain column densities (10 12 to 10 15 cm −2) and optical depths (∼ 1 or less) for each exciting transition. We conclude that the populations are far from being in thermal equilibrium. We do not observe any lines excited from the far blue wing of H Lyα , which implies that the molecular features are excited by an absorbed profile. Si IV and C IV (corrected for H 2 emission) have widths of ∼ 200 km s −1 , and an array of centroids (blueshifted lines, centered, redshifted). These characteristics are difficult to understand in the context of current models of the accretion shock. For DR Tau we observe transient strong blueshifted emission, perhaps the a result of reconnection events in the magnetosphere. We also see evidence of multiple emission regions for the hot lines. While C IV is optically thin in most stars in our sample, Si IV is not. However, C IV is a good predictor of Si IV and H 2 emission. We conclude that most of the flux in the hot lines may
A Far-Ultraviolet Atlas of Low-Resolutionhubble Space Telescopespectra of T Tauri Stars
The Astrophysical Journal, 2011
We present a far-ultraviolet (FUV) spectral atlas consisting of spectra of 91 pre-main sequence stars. Most stars in this sample were observed with the Space Telescope Imaging Spectrograph (STIS) and Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). A few archival spectra from International Ultraviolet Explorer (IUE) and the Goddard High Resolution Spectrograph (GHRS) on the HST are included for completeness. We find strong correlations among the O I λ1304 triplet, the Si IV λλ1394/1403 doublet, the C IV λ1549 doublet, and the He II λ1640 line luminosities. For classical T Tauri stars (CTTSs), we also find strong correlations between these lines and the accretion luminosity, suggesting that these lines form in processes related to accretion. These FUV line fluxes and X-ray luminosity correlate loosely with large scatters. The FUV emission also correlates well with Hα, Hβ, and Ca II K line luminosities. These correlations between FUV and optical diagostics can be used to obtain rough estimates of FUV line fluxes from optical observations. Molecular hydrogen (H 2) emission is generally present in the spectra of actively accreting CTTSs but not the weak-lined T Tauri stars (WTTSs) that are not accreting. The presence of H 2 emission in the spectrum of HD 98800 N suggests that the disk should be classified as actively accreting rather than a debris disk. We discuss the importance of FUV radiation, including the hydrogen Lyα line, on the photoevaporation of exoplanet atmospheres. We find that the Ca II/C IV flux ratios for more evolved stars are lower than those for less evolved accretors, indicating preferential depletion of refactory metals into dust grains.
Observations of T-Tauri Stars using HST-GHRS: II. Optical and Near UV lines
Arxiv preprint astro-ph/ …, 2001
We have analyzed GHRS data of eight Classical T Tauri stars (CTTSs) and one Weak T Tauri star (WTTS). The GHRS data consist of an spectral range 40Å wide centered on 2800Å. For 4 of the CTTS we have nearly simultaneous optical observations which contain Hα, Hβ, He I, NaD, and the Ca II infrared triplet. The Mg II resonance doublet is the strongest feature in the 2800Å range. This line has a fairly wide and symmetric emission component (∼ 200 to ∼ 300 km s −1 for the CTTSs), with a narrow central absorption and a wide blueshifted absorption superimposed to it. The narrow central absorption width and equivalent width are inconsistent with being due only to ISM clouds described in the literature, which lead us to conclude that it is partially due to non-LTE processes in the emission line region itself. The emission profile closely follows Hα. Its large width in CTTS cannot be due to the Stark effect and we suggest that it is due to supersonic turbulence. All the stars show blueshifted absorptions that are evidence of outflows (terminal velocities ∼ 300 km s −1), with multiple flows observed in two stars. We show evidence that the wind is not spherical, with wind signatures being stronger for lower inclinations at a given accretion rate. We briefly compare other optical lines with the hot transition region lines observed in CTTS.
The Astrophysical Journal, 2002
We have analyzed GHRS data of eight classical T Tauri stars (CTTSs) and one weak T Tauri star (WTTS). The GHRS data consist of a spectral range 40 wide centered on 2800 For four of the A A. CTTSs, we have nearly simultaneous optical observations that contain Ha, Hb, He I, Na D, and the Ca II infrared triplet. The Mg II resonance doublet is the strongest feature in the 2800 range. This line has A a fairly wide and symmetric emission component (D200È300 km s~1 for the CTTSs), with a narrow central absorption and a wide blueshifted absorption superimposed to it. The narrow central absorption width and equivalent width are inconsistent with being due only to interstellar medium clouds described in the literature, which leads us to conclude that it is partially due to non-LTE processes in the emission-line region itself. The emission proÐle closely follows Ha. Its large width in CTTSs cannot be due to the Stark e †ect, and we suggest that it is due to supersonic turbulence. All the stars show blueshifted absorptions that are evidence of outÑows (terminal velocities D300 km s~1), with multiple Ñows observed in two stars. We show evidence that the wind is not spherical, with wind signatures being stronger for lower inclinations at a given accretion rate. We brieÑy compare other optical lines with the hot transition region lines observed in CTTS.
High-Resolution Spectroscopy of T Tauri Stars
Publications of the Astronomical Society of Japan, 2009
We have conducted high-resolution spectroscopic observations of a sample of both classical and weak-line T Tauri stars embedded in the Taurus-Auriga molecular cloud using the Okayama Astrophysical Observatory's 188 cm telescope equipped with HIDES (HIgh Dispersion Echelle Spectrograph). Utilizing the ratios of equivalent widths of specific lines, we efficiently eliminated the effects of "veiling" and determined the atmospheric parameters individually for each object. Eight pairs of temperature-sensitive line-ratios were selected to derive the effective temperature with high precision and reliability. As for the surface gravity, we have developed a new method to determine the value. The method was first tested on observed spectral standards, and the derived surface gravities had a less than 5% deviation from the values in the literature. The derived surface gravities are well within the range of the assumed values for T Tauri stars.
Modelling mid-infrared molecular emission lines from T Tauri stars
Astronomy & Astrophysics, 2018
We introduce a new modelling framework including the Fast Line Tracer (FLITS) to simulate infrared line emission spectra from protoplanetary discs. This paper focusses on the mid-IR spectral region between 9.7 and 40 μm for T Tauri stars. The generated spectra contain several tens of thousands of molecular emission lines of H2O, OH, CO, CO2, HCN, C2H2, H2, and a few other molecules, as well as the forbidden atomic emission lines of S I, S II, S III, Si II, Fe II, Ne II, Ne III, Ar II, and Ar III. In contrast to previously published works, we do not treat the abundances of the molecules nor the temperature in the disc as free parameters, but use the complex results of detailed 2D PRODIMO disc models concerning gas and dust temperature structure, and molecular concentrations. FLITS computes the line emission spectra by ray tracing in an efficient, fast, and reliable way. The results are broadly consistent with R = 600 Spitzer/IRS observational data of T Tauri stars concerning line str...
X-ray spectroscopy of the weak-lined T Tauri star HD 283572
1998
We have analyzed the existing X-ray spectroscopic data for the Weak-Line T Tauri star (WTTS) HD 283572, from the ROSAT, ASCA and SAX satellites. All the data sets are well fit with an absorbed two-temperature model based on collisional ionization equilibrium. Together with the Einstein data discussed in the literature, these data sets afford a 16.5 years time span, allowing to study the short-and long-term spectroscopic and photometric variability characteristics of the X-ray emission from WTT stars. The X-ray luminosity of HD 283572 appears to vary by factors of ≃ 2 on time scales of tens of kiloseconds, within a single observations, while its average X-ray luminosity has varied by a factor of ≃ 2.5 (peak-to-peak) along the 16.5 yr studied here. The SAX observation also shows evidence for a short flare, with an enhancement of the X-ray luminosity by a factor of ≃ 4.
ACCRETION RATES FOR T TAURI STARS USING NEARLY SIMULTANEOUS ULTRAVIOLET AND OPTICAL SPECTRA
The Astrophysical Journal, 2013
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, η Chamaeleon and the TW Hydra Association. For each source we calculate the accretion rate (Ṁ ) 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 ofṀ 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 theṀ estimates, to produce correlations between accretion indicators (Hβ, Ca II K, C II] and Mg II) and accretion properties obtained simultaneously.
ASTRONOMY AND ASTROPHYSICS UV (IUE) spectra of the central stars of high latitude
2001
Abstract. We present an analysis of the UV (IUE) spectra of the central stars of Hb7 and Sp3. Comparison with the IUE spectrum of the standard star HD 93205 leads to a spectral classification of O3V for these stars, with an effective temperature of 50,000 K. From the P-Cygni profiles of CIV (1550˚A), we derive stellar wind velocities and mass loss rates of −1317 kms −1 ± 300 kms −1 and 2.9X10 −8 M⊙ yr −1 and −1603 kms −1 ±400 kms −1 and 7X10 −9 M ⊙ yr −1 for Hb7 and Sp3 respectively. From all the available data, we reconstruct the spectral energy distribution of Hb7 and Sp3.
Monthly Notices of the Royal Astronomical Society, 2014
The C II] feature at ∼ 2325Å is very prominent in the spectra of T Tauri stars (TTSs). This feature is a quintuplet of semiforbidden transitions excited at electron temperatures around 10,000 K that, together with the nearby Si II] and Fe II] features, provides a reliable optically thin tracer for accurate measurement of the plasma properties in the magnetospheres of TTSs. The spectra of 20 (out of 27) TTSs observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope have good enough signal-to-noise-ratio at the C II] wavelength. For these stars, we have determined electron densities (n e ) and temperatures (T e ) in the line emission region as well as the profile broadening (σ). For most of the stars in the sample (17) we obtain 10 4.1 T e 10 4.5 K and 10 8 n e 10 12 cm −3 . These stars have suprathermal line broadening (35 σ 165 km s −1 ), except TW Hya and CY Tau with thermal line broadening. Both C II] line luminosity and broadening are found to correlate with the accretion rate. Line emission seems to be produced in the magnetospheric accretion flow, close to the disc. There are three exceptions: DG Tau, RY Tau and FU Ori. The line centroids are blueshifted indicating that the line emission in these three stars is dominated by the outflow.