A tidally interacting disk in the young triple system WL 20?

We present high-resolution λ = 2.7 mm imaging of the close triple pre-main-sequence system WL 20. Compact dust emission with integrated flux density of 12.9 ± 1.3 mJy is associated with two components of the triple system, WL 20W and WL 20S. No emission above a 3 σ level of 3.9 mJy is detected toward the third component, WL 20E, which lies 3."17 (400 AU) due east in projection from its neighbors. A possibly warped structure of ~0.1 M_☉ and ≤3."2 extent encompasses WL 20W and WL 20S, which have a projected separation of 2."25 (~280 AU) along a north-south axis. This structure is most likely a tidally disrupted disk surrounding WL 20S. New near-infrared spectra of the individual components show a remarkable similarity between the two T Tauri stars of the system: WL 20E has a K7 spectral type (T_eff = 4040 K) with r_K = 0.2, and WL 20W has an M0 spectral type (T_eff = 3800 K) with r_K = 0.2. The spectrum of WL 20S is consistent with that of a source intrinsically similar to WL 20W, with r_K < 0.9, but seen through an A_V = 25 in addition to the A_V = 16.3 to the system as a whole. Taken together, these millimeter and infrared data help explain the peculiar nature of the infrared companion, WL 20S, as resulting from a large enhancement in its dusty, circumstellar environment in relation to its companions

High Resolution Near-Infrared Spectra of Protostars

We present new high resolution (R = 21,000) near-infrared (2 microns) spectroscopic observations of a sample of Class I and flat-spectrum protostellar objects in the rho Ophiuchi dark cloud. None of the five Class I spectra show CO v = 0 -- 2 absorption features, consistent with high K-band continuum veilings, 4 <= r_k <= 20 and fast stellar rotation, assuming that the underlying protostellar photospheres are of late spectral type, as is suggested by the low luminosities of most of these objects. Two of the flat-spectrum protostellar objects also show no absorption features and are likely to be highly veiled. The remaining two flat-spectrum sources show weak, broad absorptions which are consistent with an origin in quickly rotating (v sin i ~ 50 km / s) late-type stellar photospheres which are also strongly veiled, r_k = 3 - 4. These observations provide further evidence that: 1)-Class I sources are highly veiled at near-infrared wavelengths, confirming previous findings of lower resolution spectroscopic studies; and 2)- flat-spectrum protostars rotate more rapidly than classical T Tauri stars (Class II sources), supporting findings from a recent high resolution spectroscopic study of other flat-spectrum sources in this cloud. In addition our observations are consistent with the high rotation rates derived for two of the Class I protostellar objects in our sample from observations of variable hard X-ray emission obtained with the ASCA satellite. These observations suggest that certain Class I sources can rotate even more rapidly than flat-spectrum protostars, near breakup velocity.Comment: 16 pages including 2 tables and 2 figures (AASTeX 5.x) to be published in The Astronomical Journal July 200

High Resolution Near-Infrared Spectroscopy of FUors and FUor-like stars

We present new high resolution (R=18,000) near-infrared spectroscopic observations of a sample of classical FU Orionis stars (FUors) and other young stars with FUor characteristics that are sources of Herbig-Haro flows. Spectra are presented for the region 2.203 - 2.236 microns which is rich in absorption lines sensitive to both effective temperatures and surface gravities of stars. Both FUors and FUor-like stars show numerous broad and weak unidentified spectral features in this region. Spectra of the 2.280 - 2.300 micron region are also presented, with the 2.2935 micron v=2-0 CO absorption bandhead being clearly the strongest feature seen in the spectra all FUors and Fuor-like stars. A cross-correlation analysis shows that FUor and FUor-like spectra in the 2.203 - 2.236 micron region are not consistent with late-type dwarfs, giants, nor embedded protostars. The cross-correlations also show that the observed FUor-like Herbig-Haro energy sources have spectra that are substantively similar to those of FUors. Both object groups also have similar near-infrared colors. The large line widths and double-peaked nature of the spectra of the FUor-like stars are consistent with the established accretion disk model for FUors, also consistent with their near-infrared colors. It appears that young stars with FUor-like characteristics may be more common than projected from the relatively few known classical FUors.Comment: 21 pages, 4 figures, accepted by The Astronomical Journa

The MASSIVE Survey - III. Molecular gas and a broken Tully-Fisher relation in the most massive early-type galaxies

In this work we present CO(1-0) and CO(2-1) observations of a pilot sample of 15 early-type galaxies (ETGs) drawn from the MASSIVE galaxy survey, a volume-limited integral-field spectroscopic study of the most massive ETGs ($M_* >10^{11.5}M_\odot$) within 108 Mpc. These objects were selected because they showed signs of an interstellar medium and/or star formation. A large amount of gas ($>$2$\times$10$^8$ M$_{\odot}$) is present in 10 out of 15 objects, and these galaxies have gas fractions higher than expected based on extrapolation from lower mass samples. We tentatively interpret this as evidence that stellar mass loss and hot halo cooling may be starting to play a role in fuelling the most massive galaxies. These MASSIVE ETGs seem to have lower star-formation efficiencies (SFE=SFR/M$_{\rm H2}$) than spiral galaxies, but the SFEs derived are consistent with being drawn from the same distribution found in other lower mass ETG samples. This suggests that the SFE is not simply a function of stellar mass, but that local, internal processes are more important for regulating star formation. Finally we used the CO line profiles to investigate the high-mass end of the Tully-Fisher relation (TFR). We find that there is a break in the slope of the TFR for ETGs at high masses (consistent with previous studies). The strength of this break correlates with the stellar velocity dispersion of the host galaxies, suggesting it is caused by additional baryonic mass being present in the centre of massive ETGs. We speculate on the root cause of this change and its implications for galaxy formation theories.Comment: 13 pages, 7 figures, accepted by MNRA

Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

We present the first spectrum of a highly veiled, strongly accreting protostar which shows photospheric absorption features and demonstrates the stellar nature of its central core. We find the spectrum of the luminous (L_bol = 10 L_sun) protostellar source, YLW 15, to be stellar-like with numerous atomic and molecular absorption features, indicative of a K5 IV/V spectral type and a continuum veiling r_k = 3.0. Its derived stellar luminosity (3 L_sun) and stellar radius (3.1 R_sun) are consistent with those of a 0.5 M_sun pre-main-sequence star. However, 70% of its bolometric luminosity is due to mass accretion, whose rate we estimate to be 1.6 E-6 M_sun / yr onto the protostellar core. We determine that excess infrared emission produced by the circumstellar accretion disk, the inner infalling envelope, and accretion shocks at the surface of the stellar core of YLW 15 all contribute signifi- cantly to its near-IR continuum veiling. Its projected rotation velocity v sin i = 50 km / s is comparable to those of flat-spectrum protostars but considerably higher than those of classical T Tauri stars in the rho Oph cloud. The protostar may be magnetically coupled to its circumstellar disk at a radius of 2 R_*. It is also plausible that this protostar can shed over half its angular momentum and evolve into a more slowly rotating classical T Tauri star by remaining coupled to its circumstellar disk (at increasing radius) as its accretion rate drops by an order of magnitude during the rapid transition between the Class I and Class II phases of evolution. The spectrum of WL 6 does not show any photospheric absorption features, and we estimate that its continuum veiling is r_k >= 4.6. Together with its low bolometric luminosity (2 L_sun), this dictates that its central core is very low mass, ~0.1 M_sun.Comment: 14 pages including 9 figures (3 figures of 3 panels each, all as separate files). AASTeX LaTex macros version 5.0. To be published in The Astronomical Journal (tentatively Oct 2002

James Webb Space Telescope (JWST) and Star Formation

The 6.5-m aperture James Webb Space Telescope (JWST) will be a powerful tool for studying and advancing numerous areas of astrophysics. Its Fine Guidance Sensor, Near-Infrared Camera, Near-Infrared Spectrograph, and Mid-Infrared Instrument will be capable of making very sensitive, high angular resolution imaging and spectroscopic observations spanning 0.7 - 28 ?m wavelength. These capabilities are very well suited for probing the conditions of star formation in the distant and local Universe. Indeed, JWST has been designed to detect first light objects as well as to study the fine details of jets, disks, chemistry, envelopes, and the central cores of nearby protostars. We will be able to use its cameras, coronagraphs, and spectrographs (including multi-object and integral field capabilities) to study many aspects of star forming regions throughout the galaxy, the Local Group, and more distant regions. I will describe the basic JWST scientific capabilities and illustrate a few ways how they can be applied to star formation issues and conditions with a focus on Galactic regions

The MASSIVE Survey - VIII. Stellar Velocity Dispersion Profiles and Environmental Dependence of Early-Type Galaxies

We measure the radial profiles of the stellar velocity dispersions, $\sigma(R)$, for 90 early-type galaxies (ETGs) in the MASSIVE survey, a volume-limited integral-field spectroscopic (IFS) galaxy survey targeting all northern-sky ETGs with absolute $K$-band magnitude $M_K < -25.3$ mag, or stellar mass $M_* > 4 \times 10^{11} M_\odot$, within 108 Mpc. Our wide-field 107" $\times$ 107" IFS data cover radii as large as 40 kpc, for which we quantify separately the inner (2 kpc) and outer (20 kpc) logarithmic slopes $\gamma_{\rm inner}$ and $\gamma_{\rm outer}$ of $\sigma(R)$. While $\gamma_{\rm inner}$ is mostly negative, of the 56 galaxies with sufficient radial coverage to determine $\gamma_{\rm outer}$ we find 36% to have rising outer dispersion profiles, 30% to be flat within the uncertainties, and 34% to be falling. The fraction of galaxies with rising outer profiles increases with $M_*$ and in denser galaxy environment, with 10 of the 11 most massive galaxies in our sample having flat or rising dispersion profiles. The strongest environmental correlations are with local density and halo mass, but a weaker correlation with large-scale density also exists. The average $\gamma_{\rm outer}$ is similar for brightest group galaxies, satellites, and isolated galaxies in our sample. We find a clear positive correlation between the gradients of the outer dispersion profile and the gradients of the velocity kurtosis $h_4$. Altogether, our kinematic results suggest that the increasing fraction of rising dispersion profiles in the most massive ETGs are caused (at least in part) by variations in the total mass profiles rather than in the velocity anisotropy alone.Comment: Accepted/in press, MNRA