458 research outputs found
Maps of millimeter wave emission from three galactic star-forming regions
In order to investigate the gas dynamics around young stellar objects, three sources were mapped which exhibit supersonic velocities in the 115 GHZ, J = 1-0 transition of CO. The maps, made with the Owens Valley Radio Observatory Millimeter Interferometer, are the highest spatial resolution images currently available of millimeter-wave continuum and line emission from the sources S106, S87, and LkHalpha101. Observations were made in the CS (J = 2-1) and C-13O (J = 1-0) transitions. In all the sources, the observations indicate that the ionized stellar wind is sweeping up ambient molecular gas. The molecular gas is found adjacent to the outer edges of the ionized winds, which originate in embedded infrared sources. From the observations presented, it may be inferred that the outflowing ionized winds are channeled by the surrounding dense, neutral gas
A Luminous Infrared Companion in the Young Triple System WL 20
We present spatially resolved near-infrared and mid-infrared (1-25 microns)
imaging of the WL 20 triple system in the nearby (d=125 pc) rho Ophiuchi
star-forming cloud core. We find WL 20 to be a new addition to the rare class
of "infrared companion systems", with WL 20:E and WL 20:W displaying Class II
(T-Tauri star) spectral energy distributions (SEDs) and total luminosities of
0.61 and 0.39 L_sun, respectively, and WL 20:S, the infrared companion, with a
Class I (embedded protostellar) SED and a luminosity of 1.0-1.8 L_sun. WL 20:S
is found to be highly variable over timescales of years, to be extended (40 AU
diameter) at mid-infrared wavelengths, and to be the source of the centimeter
emission in the system. The photospheric luminosities, estimated from our data,
allow us to compare and test current pre-main-sequence evolutionary tracks. WL
20:E and WL 20:W fall into the region of the H-R diagram in which sources may
appear up to twice as old as they actually are using non-accreting tracks, a
fact which may reconcile the co-existence of two T-Tauri stars with an embedded
protostar in a triple system. The derived masses and observed projected
separations of the components of the WL 20 triple system indicate that it is in
an unstable dynamical configuration, and may therefore provide an example of
dynamical evolution during the pre-main-sequence phase.Comment: AASTeX 5.0, 17 pages, 4 tables, 9 figures, accepted by AJ, to appear
Feb. 200
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
IRS Scan-mapping of the Wasp-waist Nebula (IRAS 16253–2429). I. Derivation of Shock Conditions from H_2 Emission and Discovery of 11.3 μm PAH Absorption
The outflow driven by the Class 0 protostar, IRAS 16253–2429, is associated with bipolar cavities visible in scattered mid-infrared light, which we refer to as the Wasp-Waist Nebula. InfraRed Spectometer (IRS) scan mapping with the Spitzer Space Telescope of a ~1' × 2' area centered on the protostar was carried out. The outflow is imaged in six pure rotational (0-0 S(2) through 0-0 S(7)) H_2 lines, revealing a distinct, S-shaped morphology in all maps. A source map in the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature is presented in which the protostellar envelope appears in absorption. This is the first detection of absorption in the 11.3 μm PAH feature. Spatially resolved excitation analysis of positions in the blue- and redshifted outflow lobes, with extinction-corrections determined from archival Spitzer 8 μm imaging, shows remarkably constant temperatures of ~1000 K in the shocked gas. The radiated luminosity in the observed H_2 transitions is found to be 1.94 ± 0.05 × 10^(–5) L_⊙ in the redshifted lobe and 1.86 ± 0.04 × 10^(–5) L_⊙ in the blueshifted lobe. These values are comparable to the mechanical luminosity of the flow. By contrast, the mass of hot (T ~ 1000 K) H_2 gas is 7.95 ± 0.19 × 10^(–7) M_⊙ in the redshifted lobe and 5.78 ± 0.17 × 10^(–7) M_⊙ in the blueshifted lobe. This is just a tiny fraction, of order 10^(–3), of the gas in the cold (30 K), swept-up gas mass derived from millimeter CO observations. The H_2 ortho/para ratio of 3:1 found at all mapped points in this flow suggests previous passages of shocks through the gas. Comparison of the H_2 data with detailed shock models of Wilgenbus et al. shows the emitting gas is passing through Jump (J-type) shocks. Pre-shock densities of 10^4 cm^(–3)≤ n _H ≤ 10^5 cm^(–3) are inferred for the redshifted lobe and n _H ≤ 10^3 cm^(–3) for the blueshifted lobe. Shock velocities are 5 km s^(–1) ≤ v_s ≤ 10 km s^(–1) for the redshifted gas and v_s = 10 km s^(–1) for the blueshifted gas. Initial transverse (to the shock) magnetic field strengths for the redshifted lobe are in the range 10-32 μG, and just 3 μG for the blueshifted lobe. A cookbook for using the CUBISM contributed software for IRS spectral mapping data is presented in the Appendix
First Evidence of a Precessing Jet Excavating a Protostellar Envelope
We present new, sensitive, near-infrared images of the Class I protostar,
Elias 29, in the Ophiuchus cloud core. To explore the relationship between the
infall envelope and the outflow, narrowband H2 1-0 S(1), Br-gamma, and
narrowband K-continuum filters were used to image the source with the
Wide-Field Infrared Camera on the Hale 5m telescope and with Persson's
Auxiliary Nasmyth Infrared Camera on the Baade 6.5 m telescope. The source
appears as a bipolar, scattered light nebula, with a wide opening angle in all
filters, as is typical for late-stage protostars. However, the pure H2
emission-line images point to the presence of a heretofore undetected
precessing jet. It is argued that high-velocity, narrow, precessing jets
provide the mechanism for creating the observed wide-angled outflow cavity in
this source.Comment: 11 pages, 1 figure, 1 tabl
Accretion in the Rho-Oph pre-main sequence stars
The aim of this paper is to provide a measurement of the mass accretion rate
in a large, complete sample of objects in the core of the star forming region
Rho-Oph. The sample includes most of the objects (104 out of 111) with evidence
of a circumstellar disk from mid-infrared photometry; it covers a stellar mass
range from about 0.03 to 3 Msun and it is complete to a limiting mass of ~0.05
Msun. We used J and K-band spectra to derive the mass accretion rate of each
object from the intensity of the hydrogen recombination lines, Pab or Brg. For
comparison, we also obtained similar spectra of 35 diskless objects. The
results show that emission in these lines is only seen in stars with disks, and
can be used as an indicator of accretion. However, the converse does not hold,
as about 50% of our disk objects do not have detectable line emission. The
measured accretion rates show a strong correlation with the mass of the central
object (Macc ~ Mstar^1.8+-0.2) and a large spread, of two orders of magnitude
at least, for any interval of Mstar. A comparison with existing data for Taurus
shows that the objects in the two regions have similar behaviour, at least for
objects more massive than ~0.1Msun. The implications of these results are
briefly discussed.Comment: A&A in press, 16 pages including tables, 5 figure
A Significant Population of Candidate New Members of the ρ Ophiuchi Cluster
We present a general method for identifying the pre-main-sequence population of any star-forming region, unbiased with respect to the presence or absence of disks, in contrast to samples selected primarily via their mid-infrared emission from Spitzer surveys. We have applied this technique to a new, deep, wide-field, near-infrared imaging survey of the ρ Ophiuchi cloud core to search for candidate low-mass members. In conjunction with published Spitzer IRAC photometry and least-squares fits of model spectra (COND, DUSTY, NextGen, and blackbody) to the observed spectral energy distributions, we have identified 948 candidate cloud members within our 90% completeness limits of J = 20.0, H = 20.0, and Ks = 18.50. This population represents a factor of ~3 increase in the number of known young stellar objects in the ρ Ophiuchi cloud. A large fraction of the candidate cluster members (81% ± 3%) exhibit infrared excess emission consistent with the presence of disks, thus strengthening the possibility of their being bona fide cloud members. Spectroscopic follow-up will confirm the nature of individual objects, better constrain their parameters, and allow an initial mass function to be derived
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