We analyze the HCO{sup +} 3-2 and H{sup 13}CO{sup +} 3-2 line profiles of 27 high-mass star-forming regions to identify asymmetries that are suggestive of mass inflow. Three quantitative measures of ...line asymmetry are used to indicate whether a line profile is blue, red, or neither-the ratio of the temperature of the blue and red peaks, the line skew, and the dimensionless parameter {delta}v. We find nine HCO{sup +} 3-2 line profiles with a significant blue asymmetry and four with significant red asymmetric profiles. Comparing our HCO{sup +} 3-2 results to HCN 3-2 observations from Wu et al., we find that eight of the blue and three of the red have profiles with the same asymmetry in HCN. The eight sources with blue asymmetries in both tracers are considered strong candidates for inflow. Quantitative measures of the asymmetry (e.g., {delta}v) tend to be larger for HCN. This, combined with possible HCO{sup +} abundance enhancements in outflows, suggests that HCN may be a better tracer of inflow. Understanding the behavior of common molecular tracers like HCO{sup +} in clumps of different masses is important for properly analyzing the line profiles seen in a sample of sources representing a broad range of clump masses. Such studies will soon be possible with the large number of sources with possible self-absorption seen in spectroscopic follow-up observations of clumps identified in the Bolocam Galactic Plane Survey.
Most stars and thus most planetary systems do not form in isolation. The larger star-forming environment affects protoplanetary disks in multiple ways: gravitational interactions with other stars ...truncate disks and alter the architectures of exoplanet systems; external irradiation from nearby high-mass stars truncates disks and shortens their lifetimes; and remaining gas and dust in the environment affects dynamical evolution (if removed by feedback processes) and provides some shielding for disks from external irradiation. The dynamical evolution of the region regulates when and how long various feedback mechanisms impact protoplanetary disks. Density is a key parameter that regulates the intensity and duration of UV irradiation and the frequency of dynamical encounters. The evolution of larger star-forming complexes may also play an important role by mixing populations. Observations suggest that clusters are not a single-age population but multiple populations with small age differences which may be key to resolving several timescale issues (i.e., proplyd lifetimes, enrichment). In this review, we consider stellar clusters as the ecosystems in which most stars and therefore most planets form. We review recent observational and theoretical results and highlight upcoming contributions from facilities expected to begin observations in the next five years. Looking further ahead, we argue that the next frontier is large-scale surveys of low-mass stars in more distant high-mass star-forming regions. The future of ecosystem studies is bright as faint low-mass stars in more distant high-mass star-forming regions will be routinely observable in the era of Extremely Large Telescopes (ELTs).
Fellow Supervisor Bill Willson filed a complaint with police late last year alleging Mr. Yerke repeatedly made obscene gestures toward him, including times when Mr. Yerke was allegedly plowing ...township roads with Covington equipment.
We present new spectroscopy and Hubble Space Telescope imaging of protostellar jets discovered in an Hα survey of the Carina Nebula. Near-IR Fe II emission from these jets traces dense gas that is ...self-shielded from Lyman continuum photons from nearby O-type stars, but is excited by non-ionizing FUV photons that penetrate the ionization front within the jet. New near-IR Fe II images reveal a substantial mass of dense, neutral gas that is not seen in Hα emission from these jets. In some cases, Fe II emission traces the jet inside its natal dust pillar, connecting the larger Hα outflow to the embedded IR source that drives it. New proper motion measurements reveal tangential velocities similar to those typically measured in lower-luminosity sources (100 – 200 km s-1). Combining high jet densities and fast outflow speeds leads to mass-loss rate estimates an order of magnitude higher than those derived from the Hα emission measure alone. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (∼ 2 – 8 Mspecial character omitted protostars. For some sources, the mid-IR luminosities of the driving sources are clearly consistent with intermediate-mass protostars; others remain deeply embedded and require long-wavelength, high-resolution images to confirm their luminosity. These outflows are all highly collimated, with opening angles of only a few degrees. With this new view of collimated jets from intermediate-mass protostars, we argue that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core and the material it sweeps up are irradiated and rendered observable. Thus, the jets in Carina offer strong additional evidence that stars up to ∼ 8 Mspecial character omitted form by the same accretion mechanisms as low-mass stars.
Spitzer IRAC Observations of AGB Stars Marengo, Massimo; Reiter, Megan; Fazio, Giovanni G
The Ninth Torino Workshop on Evolution and Nucleosynthesis in AGB Stars and the Second Perugia Workshop on Nuclear Astrophysics (AIP Conference Proceedings Volume 1001),
01/2008, Letnik:
1001
Journal Article
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We present here the first observation of galactic AGB stars with the InfraRed Array Camera (IRAC) onboard the Spitzer Space Telescope. Our sample consists of 48 AGB stars of different chemical ...signature, mass loss rate and variability class. For each star we have measured IRAC photometry and colors. Preliminary results shows that IRAC colors are sensitive to spectroscopic features associated to molecules and dust in the AGB wind. Period is only loosely correlated to the brightness of the stars in the IRAC bands. We do find, however, a tight period-color relation for sources classified as 'semiregular' variables. This may be interpreted as the lack of warm dust in the wind of the sources in this class, as opposed to Mira variables that show higher infrared excess in all IRAC bands.
Understanding how the birthplace of stars affects planet-forming discs is important for a comprehensive theory of planet formation. Most stars are born in dense star-forming regions where the ...external influence of other stars, particularly the most massive stars, will affect the survival and enrichment of their planet-forming discs. Simulations suggest that stellar dynamics play a central role in regulating how external feedback affects discs, but comparing models to observations requires an estimate of the initial stellar density in star-forming regions. Structural analyses constrain the amount of dynamical evolution a star-forming region has experienced; regions that maintain substructure and do not show mass segregation are likely dynamically young, and therefore close to their birth density. In this paper, we present a structural analysis of two clusters in the Carina Nebula, Tr14 and Tr16. We show that neither cluster shows evidence for mass segregation or a centrally concentrated morphology, suggesting that both regions are dynamically young. This allows us to compare to simulations from Nicholson et al. (2019) who predict disc survival rates in star-forming regions of different initial densities. The surviving disc fractions in Tr14 and Tr16 are consistent with their predictions (both are \(\sim 10\)%), supporting a growing body of evidence that the star-forming environment plays an important role in the survival and enrichment of protoplanetary discs.
The canonical picture of star formation involves disk-mediated accretion,
with Keplerian accretion disks and associated bipolar jets primarily observed
in nearby, low-mass young stellar objects ...(YSOs). Recently, rotating gaseous
structures and Keplerian disks have been detected around a number of massive (M
> 8 solar masses) YSOs (MYSOs) including several disk-jet systems. All of the
known MYSO systems are located in the Milky Way, and all are embedded in their
natal material. Here we report the detection of a rotating gaseous structure
around an extragalactic MYSO in the Large Magellanic Cloud. The gas motions
show radial flow of material falling from larger scales onto a central
disk-like structure, the latter exhibiting signs of Keplerian rotation, i.e., a
rotating toroid feeding an accretion disk and thus the growth of the central
star. The system is in almost all aspects comparable to Milky Way high-mass
young stellar objects accreting gas via a Keplerian disk. The key difference
between this source and its Galactic counterparts is that it is optically
revealed, rather than being deeply embedded in its natal material as is
expected of such a young massive star. We suggest that this is the consequence
of the star having formed in a low-metallicity and low-dust content
environment, thus providing important constraints for models of the formation
and evolution of massive stars and their circumstellar disks.
We present deep 1.4-4.8 um JWST-NIRCam imaging of the Serpens Main star-forming region and identify 20 candidate protostellar outflows, most with bipolar structure and identified driving sources. The ...outflow position angles (PAs) are strongly correlated, and aligned within +/- 24 degrees of the major axis of the Serpens filament. These orientations are further aligned with the angular momentum vectors of the two disk shadows in this region. We estimate that the probability of this number of young stars being co-aligned if sampled from a uniform PA distribution is 10^-4. This in turn suggests that the aligned protostars, which seem to be at similar evolutionary stages based on their outflow dynamics, formed at similar times with a similar spin inherited from a local cloud filament. Further, there is tentative evidence for a systematic change in average position angle between the north-western and south-eastern cluster, as well as increased scatter in the PAs of the south-eastern protostars. SOFIA-HAWC+ archival dust polarization observations of Serpens Main at 154 and 214 um are perpendicular to the dominant jet orientation in NW region in particular. We measure and locate shock knots and edges for all of the outflows and provide an identifying catalog. We suggest that Serpens main is a cluster that formed from an isolated filament, and due to its youth retains its primordial outflow alignment.
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