A survey and analysis of Spitzer infrared spectrograph spectra of T Tauri stars in Taurus (original) (raw)
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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.
The SPITZER c2d Survey of Weak‐Line T Tauri Stars. I. Initial Results
The Astrophysical Journal, 2006
Using the Spitzer Space Telescope, we have observed 90 weak-line and classical T Tauri stars in the vicinity of the Ophiuchus, Lupus, Chamaeleon, and Taurus star-forming regions as part of the Cores to Disks (c2d) Spitzer Legacy project. In addition to the Spitzer data, we have obtained contemporaneous optical photometry to assist in constructing spectral energy distributions. These objects were specifically chosen as solar-type young stars with low levels of H emission, strong X-ray emission, and lithium absorption, i.e., weak-line T Tauri stars, most of which were undetected in the mid-to far-IR by the IRAS survey. Weak-line T Tauri stars are potentially extremely important objects in determining the timescale over which disk evolution may take place. Our objective is to determine whether these young stars are diskless or have remnant disks that are below the detection threshold of previous infrared missions. We find that only 5/83 weak-line T Tauri stars have detectable excess emission between 3.6 and 70 m, which would indicate the presence of dust from the inner few tenths of an AU out to the planetforming regions a few tens of AU from the star. Of these sources, two have small excesses at 24 m consistent with optically thin disks; the others have optically thick disks already detected by previous IR surveys. All of the seven classical T Tauri stars show excess emission at 24 and 70 m although their properties vary at shorter wavelengths. Our initial results show that disks are rare among young stars selected for their weak H emission.
An Infrared/X-Ray Survey for New Members of the Taurus Star-Forming Region
The Astrophysical Journal, 2009
We present the results of a search for new members of the Taurus star-forming region using data from the Spitzer Space Telescope and the XMM-Newton Observatory. We have obtained optical and near-infrared spectra of 44 sources that exhibit red Spitzer colors that are indicative of stars with circumstellar disks and 51 candidate young stars that were identified by Scelsi and coworkers using XMM-Newton. We also performed spectroscopy on four possible companions to members of Taurus that were reported by Kraus and Hillenbrand. Through these spectra, we have demonstrated the youth and membership of 41 sources, 10 of which were independently confirmed as young stars by Scelsi and coworkers. Five of the new Taurus members are likely to be brown dwarfs based on their late spectral types (>M6). One of the brown dwarfs has a spectral type of L0, making it the first known L-type member of Taurus and the least massive known member of the region (M ∼ 4-7 M Jup). Another brown dwarf exhibits a flat infrared spectral energy distribution, which indicates that it could be in the protostellar class I stage (star+disk+envelope). Upon inspection of archival images from various observatories, we find that one of the new young stars has a large edge-on disk (r = 2. ′′ 5 = 350 AU). The scattered light from this disk has undergone significant variability on a time scale of days in optical images from the Canada-France-Hawaii Telescope. Using the updated census of Taurus, we have measured the initial mass function for the fields observed by XMM-Newton. The resulting mass function is similar to previous ones that we have reported for Taurus, showing a surplus of stars at spectral types of K7-M1 (0.6-0.8 M ⊙) relative to other nearby star-forming regions like IC 348, Chamaeleon I, and the Orion Nebula Cluster.
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.
Photometry and spectroscopy of RV Tauri stars
2020
RV Tauri stars are recognized as radially pulsating, post-Asymptotic Giant Branch stars, in the high-luminosity end of type-II Cepheids. They show characteristic light modulations and spectral line variations which are generally linked with intrinsic radial pulsations and resulting shock waves. This thesis investigates stellar pulsations in a sample of RV Tauri stars using a mix of analytical methods. In particular, it examines the short-term and long-term variability by searching for periodicities in the photometric and spectroscopic data for a number of selected southern hemisphere RV Tauri stars. These data are used to explore how the variability and other observed stellar properties, fit within the current theories which explain RV Tauri behaviour as being due to stellar pulsation, binarity, and interaction with its local environment, including circumbinary dust. We use extensive visual photometric data from the AAVSO International Database for analysing the long-term and short-term variations and recent BV data for analysing the short-term pulsations. AAVSO's VPhot was used to perform differential photometry for the BV data and Period04 was used for Fourier analysis and least-squares fitting in a pre-whitening manner to find periodicites in both visual and BV data. Both short-term pulsational and most of the long-term periods of all the stars studied were found to be in reasonable agreement with the published values. The amplitude of the long-term periods was substantial in variation. Complex peak structures are seen in periodograms possibly owing to period changes over time and/or "flips" seen in the deep-shallow light curve alternation with time. These variations in both short and long-term periods (and also amplitude) over time is confirmed in wavelet analysis of U Mon and IW Car. Nearly 100 spectra of U Mon were acquired over 5 months to cover ∼1.5 cycles of its 92-day pulsation period. Effects of two pulsation-related shock-waves per pulsation cycle were seen on specific spectral line profiles, consistent with previous studies. The new pulsational radial velocity curves measured by Gaussian profile fitting to the Fe I line at 6200.313Å show well-defined consistency with the published pulsational radial velocity curve. The results in this thesis add depth and scope to the leading RV Tauri model which explains the light and spectral variations in RVb stars through a combination of binarity, intrinsic stellar pulsations, interaction and obscuration mechanisms involving binaries and circumstellar/circumbinary disk depending on the observer's perspective.
T Tauri Stars: The X-Ray Connection
The Non-Sleeping Universe, 1999
We have analysed newly calibrated IUE and ROSAT data for three T Tauri stars from different subclasses: TW Hya, V410 Tau and CS Cha, a Classical T Tauri star (CTTS), a Weak T Tauri star (WTTS) and a T Tauri star intermediate between CTTS and WTTS, respectively. In the ultraviolet the continuum seems to be well explained by the sum of the stellar black body emission plus a hydrogenic component with temperature in the range 1.4 to 5 × 10 4 K. TW Hya requires additionally a third component at 7900 K covering approximately 5% of the stellar surface. Using UV line fluxes, we have also analysed the energy emitted by these stars up to temperatures of 10 5 K. All three stars show emission strongly enhanced relatively to the Sun and peaking at temperatures characteristic of the transition region. In this respect the behaviour of the three stars seems to extend in a harmonic way from the ultraviolet into the X-ray band. The X-ray spectral analyses are consistent with emission from a twotemperature, optically thin plasma in collisional equilibrium. The lowest temperature plasma is at about 10 6 K while the highest reaches 10 7 K. We have also checked for and found no evidence for flaring activity in our sources at the time of the observations. Nevertheless, some level of variability is present for the stars in the sample. The ROSAT datasets for V410 Tau show a variation in terms of count rate on timescales of months to years.
The far-UV spectrum of T Tauri stars -- I. The relevance of the IUE Newly Extracted Spectra
Monthly Notices of the Royal Astronomical Society, 2000
The far-UV spectrum of the T Tauri stars (TTSs) provides important clues about the structure of the stellar atmospheres, winds and accretion shocks. The IUE (International Ultraviolet Explorer) Final Archive contains the most complete data base for such studies. A new extraction system, the IUE Newly Extracted Spectra (ines), has been developed to overcome the disadvantages of the extraction system used in the IUE Final Archive, the Signal Weighted Extraction Technique (swet). We have compared the ines spectra of the whole sample of TTSs in the far-UV range (1200±2000 A Ê) with the swet low-resolution spectra available in the IUE Final Archive. Although in most of the cases there is a good agreement between both samples, an important enhancement of the ines line fluxes with respect to the swet line fluxes is reported for particular spectra. The line fluxes are enhanced by as much as a factor of ,2.5 in some objects, which is significant for variability studies of TTSs because the variations of the UV lines are typically of this order. The emissionmeasure distributions built to study the atmospheres of these stars are based on the UV emission line fluxes, so the new system is susceptible to introduce changes in these models. Moreover, the non-linear enhancement of the ines line fluxes produces variations in diagnostic line ratios usually taken as temperature and density tracers in late-type stars. These line ratios can vary by as much as a factor of 3 when the ines data are compared with the swet, with the subsequent variation of the physical parameters derived from them.
A Survey for New Members of Taurus with the Spitzer Space Telescope
The Astrophysical Journal, 2006
We present the results of a search for new members of the Taurus star-forming region using the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope. With IRAC images of 29.7 deg 2 of Taurus at 3.6, 4.5, 5.8, and 8.0 µm, we have identified sources with red mid-infrared colors indicative of disk-bearing objects and have obtained optical and infrared spectra of 23 of these candidate members. Through this work, we have discovered 13 new members of Taurus, two of which have spectral types later than M6 and thus are likely to be brown dwarfs according to the theoretical evolutionary models of Chabrier and Baraffe. This survey indicates that the previous census of Taurus has a completeness of ∼ 80% for members with disks. The new members that we have found do not significantly modify the previously measured distributions of Taurus members as a function of position, mass, and extinction. For instance, we find no evidence for a population of highly reddened brown dwarfs (A K ∼ 2) that has been missed by previous optical and near-infrared surveys, which suggests that brown dwarf disks are not significantly more flared than disks around stars. In addition to the new members, we also present IRAC photometry for the 149 previously known members that appear within this survey, which includes 27 objects later than M6.
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 present the analysis of 42 spectra of the Classical T Tauri star TW Hya observed with the FEROS echelle spectrograph over 2 yr. We determined the rotational and radial velocities of TW Hya, obtaining v sin i ¼ 5 AE 2 km s À1 and v rad ¼ 12:5 AE 0:5 km s À1 . The star exhibits strong emission lines that show substantial variety and variability in their profile shapes. Emission lines such as H, H, and He i show both outflow and infall signatures, which change on different timescales. The system displays periodic variations in line and veiling intensities, but the stellar rotation period remains uncertain. We see evidence of a variation in the mass accretion rate over a 1 yr period from the Na D line profiles that are well fitted by magnetospheric accretion models with moderate mass accretion rates (10 À9 up to 10 À8 M yr À1 ). The lower values inferred from the models are close to the average mass accretion rate obtained from the veiling estimates (~2 Â 10 À9 M yr À1 ), but the veiling results are consistent with a constant mass accretion rate within the errors of the calculations. The H, He i, Na D, and H emission-line equivalent widths corrected from veiling correlate well with each other and are correlated with the veiling, indicating the same mechanism should be powering them and suggesting an origin related to the accretion process. The wings of the main emission lines are generally correlated, except when the Balmer lines exhibit properties suggesting a strong contribution from a wind. The blueward absorption components of the Balmer lines, most likely from a wind, are not correlated with veiling. The spectroscopic analysis allows us to infer the inclination of the stellar rotation axis (i ¼ 18 AE 10 ) that matches the current estimations of the disk orientation (0 < i < 15 ). A magnetospheric dipole axis that is misaligned with the stellar/disk rotation axis could produce the observed photometric variability, and we tend to favor a low inclination but not a totally face-on geometry for the system. TW Hya exhibits typical spectral characteristics of many classical T Tauri stars in Taurus despite its older age, indicating that active accretion disks can readily survive up to 10 Myr.