[en] We present high signal-to-noise ratio (S/N), moderate spectral resolution (R ∼ 2000-2500) near-infrared (0.8-5.0 μm) spectroscopy of the nearby T Tauri star TW Hya. By comparing the spectrum and the equivalent widths of several atomic and molecular features with those for stars in the IRTF near-infrared library, we revise the spectral type to M2.5V, which is later than what is usually adopted (K7V). This implies a substantially cooler stellar temperature than previously assumed. Comparison with various pre-main-sequence models suggests that TW Hya is only ∼3 Myr old, much younger than the usually adopted 8-10 Myr. Analysis of the relative strengths of the H lines seen in the spectrum yields estimates for the temperature and density of the emitting region of T_e ≥ 7500 K and n_e ∼ 10¹²-10¹³ cm^-3. The thickness of the emitting region is 10²-10⁴ km and the covering fraction is f_* ∼ 0.04. Our derived physical parameter values agree with the predictions of the magnetospheric accretion scenario. The highest S/N H lines have profiles that indicate multiple emission components. We derive an excess spectrum (above that of the M2.5V template) that peaks in the H band. Although our derived veiling values (∼0.1) agree with previous estimates, the excess spectrum does not match that of current models in which this flux is generated by an inner optically thin disk. We suggest that the excess flux spectrum instead reflects the differences in atmospheric opacity, gravity, and age between TW Hya and older, higher gravity, field M2.5 dwarfs.

[en] We present deep high-angular resolution observations of the high-mass protostar NGC 7538 S, which is in the center of a cold dense cloud core with a radius of 0.5 pc and a mass of ∼2000 M _sun. These observations show that NGC 7538 S is embedded in a compact elliptical core with a mass of 85-115 M _sun. The star is surrounded by a rotating accretion disk, which powers a very young, hot molecular outflow approximately perpendicular to the rotating accretion disk. The accretion rate is very high, ∼(1.4-2.8) x 10^-3 M _sun yr^-1. Evidence for rotation of the disk surrounding the star is seen in all largely optically thin molecular tracers, H¹³CN J = 1 → 0, HN¹³C J = 1 → 0, H¹³CO⁺ J = 1 → 0, and DCN J = 3 → 2. Many molecules appear to be affected by the hot molecular outflow, including DCN and H¹³CO⁺. The emission from CH₃CN, which has often been used to trace disk rotation in young high-mass stars, is dominated by the outflow, especially at higher K levels. Our new high angular resolution observations show that the rotationally supported part of the disk is smaller than we previously estimated. The enclosed mass of the inner, rotationally supported part of the disk (D ∼ 5'', i.e., 14,000 AU) is ∼14-24 M _sun.

[en] We investigate the young stellar population in and near the cometary globule Ori I-2. The analysis is based on deep Nordic Optical Telescope R-band and Hα images, JCMT SCUBA 450 and 850 μm images combined with near-infrared Two Micron All Sky Survey (2MASS) photometry and mid-infrared archival Spitzer images obtained with the Infrared Array Camera (IRAC; 3.6, 4.5, 5.8, and 8 μm), and MIPS (24 and 70 μm) instruments. We identify a total of 125 sources within the 5'x5' region imaged by the IRAC. Of these sources, 87 are detected in the R-band image and 51 are detected in the 2MASS. The detailed physical properties of the sources are explored using a combination of near/mid-infrared color-color diagrams, graybody fitting of spectral energy distributions (SEDs) and an online SED fitting tool that uses a library of two-dimensional radiation transfer based accretion models of young stellar objects with disks. Ori I-2 shows clear evidence of triggered star formation with four young low-luminosity pre-main-sequence (PMS) stars embedded in the globule. At least two, possibly as many as four, additional low-mass PMS objects were discovered in the field which are probably part of the young σ Orionis cluster. Among the PMS stars which have formed in the globule, MIR-54 is a young, deeply embedded Class 0/I object; MIR-51 and 52 are young Class II sources, while MIR-89 is a more evolved, heavily extincted Class II object with its apparent colors mimicking a Class 0/I object. The Class 0/I object MIR-54 coincides with a previously known IRAS source and is a strong submillimeter source. It is most likely the source for the molecular outflow and the large parsec-scale Herbig-Haro (HH) flow. However, the nearby Class II source, MIR-52, which is strong a Hα emission line star, also appears to drive an outflow approximately aligned with the outflow from MIR-54, and because of the proximity of the two outflows, either star could contribute. MIR-89 appears to excite a low-excitation HH object, HH 992, discovered for the first time in this study.

[en] We have acquired submillimeter observations of 33 fields containing 37 Herbig Ae/Be (HAEBE) stars or potential HAEBE stars, including SCUBA maps of all but two of these stars. Nine target stars show extended dust emission. The other 18 are unresolved, suggesting that the dust envelopes or disks around these stars are less than a few arcseconds in angular size. In several cases, we find that the strongest submillimeter emission originates from younger, heavily embedded sources rather than from the HAEBE star, which means that previous models must be viewed with caution. These new data, in combination with far-infrared flux measurements available in the literature, yield spectral energy distributions (SEDs) from far-infrared to millimeter wavelengths for all the observed objects. Isothermal fits to these SEDs demonstrate excellent fits, in most cases, to the flux densities longward of 100 μm. We find that a smaller proportion of B-type stars than A- and F-type stars are surrounded by circumstellar disks, suggesting that disks around B stars dissipate on shorter timescales than those around later spectral types. Our models also reveal that the mass of the circumstellar material and the value of β are correlated, with low masses corresponding to low values of β. Since low values of β imply large grain sizes, our results suggest that a large fraction of the mass in low-β sources is locked up in very large grains. Several of the isolated HAEBE stars have disks with very flat submillimeter SEDs. These disks may be on the verge of forming planetary systems.

[en] We have mapped the young Herbig Be star R Mon in CO(3–2) and ¹³CO(3–2) with Atacama Pathfinder EXperiment in Chile and analyzed unpublished Herschel images. We find that R Mon is embedded in a small cloud with a gas temperature of ∼20 K and a total mass of ∼70 $M_{\odot <!--\; ???\; -->}$. We confirm that R Mon drives a bipolar molecular outflow, which is blueshifted north of R Mon. The blueshifted outflow has excavated the molecular cloud north of R Mon, creating the reflection nebula NGC 2261 and filling it with high-velocity gas. At “high” velocities the orientation of the outflow is approximately n–s, which agrees with the optical jet, suggesting that the accretion disk is e–w. The outflow velocities are modest, ±9 km s⁻¹. The outflow is rather massive, ∼0.56 $M_{\odot <!--\; ???\; -->}$ in the blueshifted outflow lobe. The outflow is completely optically thick in CO(3–2) toward R Mon, indicating that its envelope is ≲2000 au. The mass of the accretion disk and surrounding envelope determined from an isothermal graybody fit is ∼0.34 $M_{\odot <!--\; ???\; -->}$. We estimate a mass-loss rate of ∼(1–3) × 10⁻⁵ $M_{\odot <!--\; ???\; -->}$ yr⁻¹, corresponding to an accretion rate of (1–9) × 10⁻⁶ $M_{\odot <!--\; ???\; -->}$ yr⁻¹. We find that R Mon has bolometric luminosity of <1000 $L_{\odot <!--\; ???\; -->}$. R Mon is still in an active accretion phase, contributing to the observed luminosity. Hence, R Mon cannot be a B0 star; it must be a late B star or even an early A star.

[en] Analysis of high spatial resolution VLA images shows that the free-free emission from NGC 7538 IRS 1 is dominated by a collimated ionized wind. We have re-analyzed high angular resolution VLA archive data from 6 cm to 7 mm, and measured separately the flux density from the compact bipolar core and the extended (1.''5-3'') lobes. We find that the flux density of the core is ∝ν^α, where ν is the frequency and α is ∼0.7. The frequency dependence of the total flux density is slightly steeper with α = 0.8. A massive optically thick hypercompact core with a steep density gradient can explain this frequency dependence, but it cannot explain the extremely broad recombination line velocities observed in this source. Neither can it explain why the core is bipolar rather than spherical, nor the observed decrease of 4% in the flux density in less than 10 yr. An ionized wind modulated by accretion is expected to vary, because the accretion flow from the surrounding cloud will vary over time. BIMA and CARMA continuum observations at 3 mm show that the free-free emission still dominates at 3 mm. HCO⁺ J = 1 → 0 observations combined with FCRAO single dish data show a clear inverse P Cygni profile toward IRS 1. These observations confirm that IRS 1 is heavily accreting with an accretion rate ∼2 x 10^-4 M _sun yr^-1.

[en] NGC 7538 IRS 1 is a very young embedded O star driving an ionized jet and accreting mass with an accretion rate >10⁻⁴ $M_{\odot <!--\; ???\; -->}$ yr⁻¹, which is quenching the hypercompact H ii region. We use SOFIA GREAT data, Herschel PACS and SPIRE archive data, SOFIA FORCAST archive data, Onsala 20 m and CARMA data, and JCMT archive data to determine the properties of the O star and its outflow. IRS 1 appears to be a single O star with a bolometric luminosity >1 × 10⁵ $L_{\odot <!--\; ???\; -->}$, i.e., spectral type O7 or earlier. We find that IRS 1 drives a large molecular outflow with the blueshifted northern outflow lobe extending to ∼280″ or 3.6 pc from IRS 1. Near IRS 1 the outflow is well aligned with the ionized jet. The dynamical timescale of the outflow is ∼1.3 × 10⁵ yr. The total outflow mass is ∼130 $M_{\odot <!--\; ???\; -->}$. We determine a mass outflow rate of 1.0 × 10⁻³ $M_{\odot <!--\; ???\; -->}$ yr⁻¹, roughly consistent with the observed mass accretion rate. We observe strong high-velocity [C ii] emission in the outflow, confirming that strong UV radiation from IRS 1 escapes into the outflow lobes and is ionizing the gas. Many O stars may form like low-mass stars, but with a higher accretion rate and in a denser environment. As long as the accretion stays high enough to quench the H ii region, the star will continue to grow. When the accretion rate drops, the H ii region will rapidly start to expand.

[en] We present high angular resolution continuum observations of the high-mass protostar NGC 7538 S with BIMA and CARMA at 3 and 1.4 mm, Very Large Array (VLA) observations at 1.3, 2, 3.5, and 6 cm, and archive Infrared Array Camera (IRAC) observations from the Spitzer Space Observatory, which detect the star at 4.5, 5.8, and 8 μm. The star looks rather unremarkable in the mid-IR. The excellent positional agreement of the IRAC source with the VLA free-free emission, the OH, CH₃OH, H₂O masers, and the dust continuum confirms that this is the most luminous object in the NGC 7538 S core. The continuum emission at millimeter wavelengths is dominated by dust emission from the dense cold cloud core surrounding the protostar. Including all array configurations, the emission is dominated by an elliptical source with a size of ∼8'' × 3''. If we filter out the extended emission we find three compact millimeter sources inside the elliptical core. The strongest one, S_A, coincides with the VLA/IRAC source and resolves into a double source at 1.4 mm, where we have subarcsecond resolution. The measured spectral index, α, between 3 and 1.4 mm is ∼2.3, and steeper at longer wavelengths, suggesting a low dust emissivity or that the dust is optically thick. We argue that the dust in these accretion disks is optically thick and estimate a mass of an accretion disk or infalling envelope surrounding S_A to be ∼60 M_☉.

[en] We present 30 and 40 μm imaging of the massive protostar G35.20–0.74 with SOFIA-FORCAST. The high surface density of the natal core around the protostar leads to high extinction, even at these relatively long wavelengths, causing the observed flux to be dominated by that emerging from the near-facing outflow cavity. However, emission from the far-facing cavity is still clearly detected. We combine these results with fluxes from the near-infrared to mm to construct a spectral energy distribution (SED). For isotropic emission the bolometric luminosity would be 3.3 × 10⁴ L_☉. We perform radiative transfer modeling of a protostar forming by ordered, symmetric collapse from a massive core bounded by a clump with high-mass surface density, Σ_cl. To fit the SED requires protostellar masses ∼20-34 M_☉ depending on the outflow cavity opening angle (35°-50°), and Σ_cl ∼ 0.4-1 g cm^–2. After accounting for the foreground extinction and the flashlight effect, the true bolometric luminosity is ∼(0.7-2.2) × 10⁵ L_☉. One of these models also has excellent agreement with the observed intensity profiles along the outflow axis at 10, 18, 31, and 37 μm. Overall our results support a model of massive star formation involving the relatively ordered, symmetric collapse of a massive, dense core and the launching bipolar outflows that clear low-density cavities. Thus a unified model may apply for the formation of both low- and high-mass stars.

[en] The Herschel Space Observatory was used to observe ∼120 pre-main-sequence stars in Taurus as part of the GASPS Open Time Key project. Photodetector Array Camera and Spectrometer was used to measure the continuum as well as several gas tracers such as [O I] 63 μm, [O I] 145 μm, [C II] 158 μm, OH, H₂O, and CO. The strongest line seen is [O I] at 63 μm. We find a clear correlation between the strength of the [O I] 63 μm line and the 63 μm continuum for disk sources. In outflow sources, the line emission can be up to 20 times stronger than in disk sources, suggesting that the line emission is dominated by the outflow. The tight correlation seen for disk sources suggests that the emission arises from the inner disk (<50 AU) and lower surface layers of the disk where the gas and dust are coupled. The [O I] 63 μm is fainter in transitional stars than in normal Class II disks. Simple spectral energy distribution models indicate that the dust responsible for the continuum emission is colder in these disks, leading to weaker line emission. [C II] 158 μm emission is only detected in strong outflow sources. The observed line ratios of [O I] 63 μm to [O I] 145 μm are in the regime where we are insensitive to the gas-to-dust ratio, neither can we discriminate between shock or photodissociation region emission. We detect no Class III object in [O I] 63 μm and only three in continuum, at least one of which is a candidate debris disk