UV-Visual Echelle Spectrograph Research Articles

Natural Coronagraphic Observations of the Eclipsing T Tauri System KH 15D: Evidence of Accretion and Bipolar Outflow in a Weak-Line T Tauri Star

We present high-resolution (R ~ 44,000) UV-Visual Echelle Spectrograph spectra of the eclipsing pre-main-sequence star KH 15D covering the wavelength range 4780-6810 A obtained at three phases: out of eclipse, near minimum light, and during egress. The system evidently acts as a natural coronagraph, enhancing the contrast relative to the continuum of hydrogen and forbidden emission lines during eclipse. At maximum light, the Hα equivalent width was ~2 A and the profile showed broad wings and a deep central absorption. During egress, the equivalent width was much higher (~70 A) and the broad wings, which extend to ±300 km s-1, were prominent. During eclipse totality, the equivalent width was less than during egress (~40 A) and the high-velocity wings were much weaker. Hβ showed a somewhat different behavior, revealing only the blueshifted portion of the high-velocity component during eclipse and egress. [O I] λλ6300, 6363 lines are easily seen both out of eclipse and when the photosphere is obscured and exhibit little or no flux variation with the eclipse phase. Our interpretation is that KH 15D, although clearly a weak-line T Tauri star by the usual criteria, is still accreting matter from a circumstellar disk and has a well-collimated bipolar jet. As the knife-edge of the occulting matter passes across the close stellar environment, it is evidently revealing structure in the magnetosphere of this pre-main-sequence star with unprecedented spatial resolution. We also show that there is only a small, perhaps marginally significant change in the velocity of the K7 star between the maximum light and egress phases probed here.

Revised Stellar Temperatures for Magellanic Cloud O Supergiants fromFar Ultraviolet Spectroscopic Explorerand Very Large Telescope UV‐Visual Echelle Spectrograph Spectroscopy

We have undertaken quantitative analysis of four LMC and SMC O4-9.7 extreme supergiants using far- ultraviolet FUSE, ultraviolet IUE/Hubble Space Telescope, and optical Very Large Telescope UV-Visual Echelle Spectrograph spectroscopy. Extended, non-LTE model atmospheres that allow for the consistent treatment of line blanketing, developed by Hillier & Miller, are used to analyze wind and photospherics spec- tral features simultaneously. Using Hto constrain mass-loss rates, He i-He ii photospheric lines reveal stel- lar temperatures that are systematically (5-7.5 kK) and substantially (15%-20%) lower than previously derived from unblanketed, plane-parallel, non-LTE photospheric studies. We have confidence in these revisions since derived temperatures generally yield consistent fits across the entire 912-7000 Aobserved spectral range. In particular, we are able to resolve the UV-optical temperature discrepancy identified for AzV 232 (O7 Iaf + ) in the SMC by Fullerton and coworkers. The temperature and abundance sensitivity of far-ultraviolet, UV, and optical lines are discussed. '' Of '' classification criteria are directly linked to (strong) nitrogen enrichment (via N iii � 4097) and (weak) carbon depletion (via C iii �� 4647-4651), providing evidence for mixing of unprocessed and CNO-processed material at their stellar surfaces. Oxygen abundances are more difficult to constrain, except via O ii lines in the O9.7 supergiant, for which it is also found to be somewhat depleted. Unfortunately, He/H is very difficult to determine in individual O super- giants because of uncertainties in microturbulence and the atmospheric scale height. The effect of wind clumping is also investigated, for which P v �� 1118-1128 potentially provides a useful diagnostic in O star winds, unless phosphorus can be independently demonstrated to be underabundant relative to other heavy elements. Revised stellar properties affect existing calibrations of (1) Lyman continuum photons—a factor of 2 lower for the O4 supergiant—and (2) kinetic energy released into the ISM by O supergiants. Our results also have importance for the calibration of the wind momentum-luminosity relationship for OB stars, particularly since the stars studied here are among the visually brightest OB stars in external galaxies. Subject headings: stars: early-type — stars: fundamental parameters — stars: mass loss — ultraviolet: stars

Kinematic Study of the Disrupting Globular Cluster Palomar 5 Using VLT Spectra

Wide-field photometric data from the Sloan Digital Sky Survey have recently revealed that the Galactic globular cluster Palomar 5 is in the process of being tidally disrupted. Here we investigate the kinematics of this sparse remote star cluster using high-resolution spectra from the Very Large Telescope (VLT). Twenty candidate cluster giants located within 6' of the cluster center have been observed with the UV-Visual Echelle Spectrograph on VLT-UT2. The spectra provide radial velocities with a typical accuracy of 0.15 km s-1. We find that the sample contains 17 certain cluster members with very coherent kinematics, two unrelated field dwarfs, and one giant with a deviant velocity, which is most likely a cluster binary showing fast orbital motion. From the confirmed members we determine the heliocentric velocity of the cluster as -58.7 ± 0.2 km s-1. The total line-of-sight velocity dispersion of the cluster stars is 1.1 ± 0.2 km s-1 (all members) or 0.9 ± 0.2 km s-1 (stars on the red giant branch only). This is the lowest velocity dispersion that has so far been measured for a stellar system classified as a globular cluster. The shape of the velocity distribution suggests that there is a significant contribution from orbital motions of binaries and that the dynamical part of the velocity dispersion is therefore still substantially smaller than the total dispersion. Comparing the observations with the results of Monte Carlo simulations of binaries we find that the frequency of binaries in Pal 5 is most likely between 24% and 63% and that the dynamical line-of-sight velocity dispersion of the cluster must be smaller than 0.7 km s-1 (90% confidence upper limit). The most probable values of the dynamical dispersion lie in the range 0.12 ≤ σ/km s-1 ≤ 0.41 (68% confidence). Pal 5 thus turns out to be a dynamically very cold system. Our results are compatible with an equilibrium system. We find that the luminosity of the cluster implies a total mass of only 4.5 to 6.0 × 103 M⊙. We further show that a dynamical line-of-sight velocity dispersion of 0.32 to 0.37 km s-1 admits a King model that fits the observed surface density profile of Pal 5 (with W0 = 2.9 and rt = 161) and its mass.

Cosmic‐Ray Production of6Li by Structure Formation Shocks in the Early Milky Way: A Fossil Record of Dissipative Processes during Galaxy Formation

While the abundances of Be and B observed in metal-poor halo stars are well explained as resulting from spallation of CNO-enriched cosmic rays (CRs) accelerated by supernova shocks, accounting for the observed 6Li in such stars with supernova CRs is more problematic. Here we propose that gravitational shocks induced by infalling and merging subgalactic clumps during hierarchical structure formation of the Galaxy should dissipate enough energy at early epochs so that the CRs accelerated by such shocks can provide a natural explanation of the observed 6Li. In clear contrast to supernovae, structure formation shocks do not eject freshly synthesized CNO nor Fe, so that ?-? fusion, which is the only effective production channel at low metallicity, is capable of generating sufficient 6Li with no accompanying Be or B and no direct correspondence with Fe. Correlations between the 6Li abundance and the kinematic properties of the halo stars may also be expected in this scenario. Further, more extensive observations of 6Li in metal-poor halo stars, e.g., by the Subaru High Dispersion Spectrograph or the Very Large Telescope UV-Visual Echelle Spectrograph, may offer us an invaluable fossil record of dissipative dynamical processes that occurred during the formation of our Galaxy.

Molecular Hydrogen, Deuterium, and Metal Abundances in the Damped Lyα System atzabs = 3.025 toward Q0347−3819

We have detected in high-resolution spectra of the quasar Q0347-3819 obtained with the UV-Visual Echelle Spectrograph (UVES) at the VLT/Kueyen telescope over 80 absorption features in the Lyman and Werner H2 bands at the redshift of a damped Lyα (DLA) system at zabs = 3.025. At the same redshift, numerous absorption lines of atoms and low ions (H I, D I, C II, C II*, N I, O I, Si II, P II, Ar I, Cr II, Fe II, and Zn II) were identified. The zabs = 3.025 system spans over ~80 km s-1 and exhibits a multicomponent velocity structure in the metal lines. The main component at zabs = 3.024855 shows a total H2 column density N(H2) = (4.10 ± 0.21) × 1014 cm-2 and a fractional molecular abundance fH2 = (1.94 ± 0.10) × 10-6 derived from the H2 lines arising from the J = 0-5 rotational levels of the ground electronic vibrational state. In the second strong component at zabs = 3.024684 we were able to set a stringent upper limit to fH2 of 3.3 × 10-9 (3 σ c.l.). The population of the J levels can be represented by a single excitation temperature of Tex = 825 ± 110 K. The ortho-H2 : para-H2 ratio equals 3.1 ± 0.3. This ratio is comparable to that calculated from hot H2 formation upon grain surfaces (ortho-H2 : para-H2 = 3 : 1) but is higher than the "freezeout" quantity (ortho-H2 : para-H2 = 1 : 4) predicted for cosmological epochs at z < 20, implying recent formation of the hydrogen molecules following photodissociation of pristine H2. In the main component the properties of the neutral atoms and low ions can be described with the same broadening parameter b ≃ 3 km s-1 of the H2 cloud. The rate at which UV photons are absorbed in the Lyman and Werner bands is found to be β0 ≃ 2 × 10-9 s-1. Taking into account that similar β0 values are observed in the Galactic diffuse molecular clouds, it shows that the UV radiation fields in the DLA and in the Milky Way are very much alike. We also found the H2 formation rate of RnH ≃ 3 × 10-16 s-1 at zabs = 3.025, which is consistent with observations in the Galactic disk diffuse clouds where nH2 is low. Comparing the relative rotational population ratios of H2 with the measured C II*/C II ratio, we can infer that nH ≃ 6 cm-3 in the main component, which gives a size of D ≃ 14 pc along the line of sight. The mean value of the dust-to-gas ratio estimated for the whole zabs = 3.025 system from the [Cr/Zn] ratio is equal to = 0.032 ± 0.005 (in units of the mean Galactic interstellar medium value). For the first time we unambiguously reveal a pronounced [α-element/iron peak] enhancement of [O,Si/Zn] = 0.6 ± 0.1 (1 σ c.l.) at high redshift. The simultaneous analysis of metal and hydrogen lines leads to D/H = (3.75 ± 0.25) × 10-5. This value is consistent with standard big bang nucleosynthesis if the baryon-to-photon ratio, η, lies within the range 4.37 × 10-10 ≲ η ≲ 5.32 × 10-10, implying 0.016 ≲ Ωbh ≲ 0.020.

High-Resolution Spectroscopy from 3050 to 10000 Å of the Hubble Deep Field South QSO J2233−606 with UVES at the ESO Very Large Telescope

We report on high-resolution observations (R 45,000) of the Hubble Deep Field South QSO J2233-606 obtained with the VLT UV-Visual Echelle Spectrograph. We present spectral data for the wavelength region 3050 A 14 has an upturn at z ~ 1.4–1.6.