We present new Spitzer/InfraRed Array Camera (IRAC) observations of 55 dusty long-period variables (48 asymptotic giant branch, AGB, and 6 red supergiant stars) in the Galaxy that have different ...chemistry, variability type, and mass-loss rate. O-rich AGB stars (including intrinsic S-type) tend to have redder 3.6-8.0 colours than carbon stars for a given 3.6-4.5 colour due to silicate features increasing the flux in the 8.0- mu m IRAC band. For colours including the 5.8 ...m band, carbon stars separate into two distinct sequences, likely due to a variable photospheric C... feature that is only visible in relatively unobscured, low mass-loss rate sources. Semiregular variables tend to have smaller infrared (IR) excess in 3.6-8.0 colour than Miras, consistent with the hypothesis that semiregular variables lose mass discontinuously. Miras have redder colours for longer periods while semiregular variables do not. Galactic AGB stars follow the period-luminosity sequences found for the Magellanic Clouds. Mira variables fall along the fundamental pulsation sequence, while semiregular variables are mostly on overtone sequences. We also derive a relationship between mass-loss rate and 3.6-8.0 colour. The fits are similar in shape to those found by other authors for AGBs in the Large Magellanic Cloud, but discrepant in overall normalization, likely due to different assumptions in the models used to derive mass-loss rates. We find that IR colours are not unique discriminators of chemical type, suggesting caution when using colour selection techniques to infer the chemical composition of AGB dust returned to the interstellar medium. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
We present new MUSE/VLT observations of a small globule in the Carina H ii region that hosts the HH 900 jet+outflow system. Data were obtained with the GALACSI ground-layer adaptive optics ...system in wide-field mode, providing spatially resolved maps of diagnostic emission lines. These allow us to measure the variation of the physical properties in the globule and jet+outflow system. We find high temperatures (Te ≈ 104 K), modest extinction (AV ≈ 2.5 mag), and modest electron densities (ne ≈ 200 cm−3) in the ionized gas. Higher excitation lines trace the ionized outflow; both the excitation and ionization in the outflow increase with distance from the opaque globule. In contrast, lower excitation lines that are collisionally de-excited at densities ≳104 cm−3 trace the highly collimated protostellar jet. Assuming the globule is an isothermal sphere confined by the pressure of the ionization front, we compute a Bonnor–Ebert mass of ∼3.7 M⊙. This is two orders of magnitude higher than previous mass estimates, calling into question whether small globules like the Tadpole contribute to the bottom of the initial mass function. The derived globule properties are consistent with a cloud that has been and/or will be compressed by the ionization front on its surface. At the estimated globule photoevaporation rate of ∼5 × 10−7 M⊙ yr−1, the globule will be completely ablated in ∼7 Myr. Stars that form in globules like the Tadpole will emerge into the H ii later and may help resolve some of the temporal tension between disc survival and enrichment.
ABSTRACT
We combine Multi-Unit Spectroscopic Explorer and Atacama Large Millimeter/sub-millimeter Array observations with theoretical models to evaluate how a tadpole-shaped globule located in the ...Carina Nebula has been influenced by its environment. This globule is now relatively small (radius ∼2500 au), hosts a protostellar jet+outflow (HH 900), and, with a blueshifted velocity of ∼10 km s−1, is travelling faster than it should be if its kinematics were set by the turbulent velocity dispersion of the precursor cloud. Its outer layers are currently still subject to heating, but comparing the internal and external pressures implies that the globule is in a post-collapse phase. Intriguingly the outflow is bent, implying that the Young Stellar Object (YSO) responsible for launching it is comoving with the globule, which requires that the star formed after the globule was up to speed since otherwise it would have been left behind. We conclude that the most likely scenario is one in which the cloud was much larger before being subject to radiatively driven implosion, which accelerated the globule to the high observed speeds under the photoevaporative rocket effect and triggered the formation of the star responsible for the outflow. The globule may now be in a quasi-steady state following collapse. Finally, the HH 900 YSO is likely ≳1 M⊙ and may be the only star forming in the globule. It may be that this process of triggered star formation has prevented the globule from fragmenting to form multiple stars (e.g. due to heating) and has produced a single higher mass star.
HH 666 is an externally irradiated protostellar outflow in the Carina nebula for which we present new near-IR Feii spectra obtained with the Folded-Port Infrared Echellette spectrograph at Magellan ...Observatory. Earlier H a and near-IR Feii imaging revealed that the two emission lines trace substantially different morphologies in the inner ~40 arcsec of the outflow. H a traces a broad cocoon that surrounds the collimated Feii jet that extends throughout the parent dust pillar. New spectra show that this discrepancy extends to their kinematics. Near-IR Feii emission traces steady, fast velocities of plus or minus 200 km s... from the eastern and western limbs of the jet. We compare this to a previously published H a spectrum that reveals a Hubble-flow velocity structure near the jet-driving source. New, second-epoch Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) H a images reveal the lateral spreading of the H a outflow lobe away from the jet axis. H a proper motions also indicate a sudden increase in the mass-loss rate ~1000 yr ago, while steady Feii emission throughout the inner jet suggest that the burst is ongoing. An accretion burst sustained for ~1000 yr is an order of magnitude longer than expected for FU Orionis outbursts, but represents only a small fraction of the total age of the HH 666 outflow. Altogether, available data suggests that Feii traces the highly collimated protostellar jet while H a traces the entrained and irradiated outflow. HH 666 appears to be a missing link between bare jets seen in H ii regions and entrained molecular outflows seen from embedded protostars in more quiescent regions. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
We present Very Large Telescope/Multi-Unit Spectroscopic Explorer Narrow Field Mode observations of a pair of disc-bearing young stellar objects towards the Orion Bar: 203–504 and 203–506. ...Both of these discs are subject to external photoevaporation, where winds are launched from their outer regions due to environmental irradiation. Intriguingly, despite having projected separation from one another of only 1.65 arcsec(660 au at 400 pc), 203–504 has a classic teardrop shaped ‘proplyd’ morphology pointing towards θ2 Ori A (indicating irradiation by the EUV of that star, rather than $\rm \theta ^1$ Ori C) but 203–506 has no ionization front, indicating it is not irradiated by stellar EUV at all. However, 203–506 does show C i 8727 Å and O i 6300 Å in emission, indicating irradiation by stellar FUV. This explicitly demonstrates the importance of FUV irradiation in driving mass loss from discs. We conclude that shielding of 203–506 from EUV is most likely due to its position on the observers side of an ionized layer lying in the foreground of the Huygens Region. We demonstrate that the outflow HH 519, previously thought to be emanating from 203–504 is actually an irradiated cloud edge and identify a new compact outflow from that object approximately along our line of sight with a velocity ∼130 km s−1.
ABSTRACT
We present new Atacama Large Millimeter/submillimeter Array observations of the tadpole, a small globule in the Carina Nebula that hosts the HH 900 jet+outflow system. Our data include 12CO, ...13CO, C18O J=2–1, 13CO, C18O J=3–2, and serendipitous detections of DCN J=3–2 and CS J=7–6. With angular resolution comparable to the Hubble Space Telescope, our data reveal for the first time the bipolar molecular outflow in CO, seen only inside the globule, that is launched from the previously unseen jet-driving protostar (the HH 900 YSO). The biconical morphology joins smoothly with the externally irradiated outflow seen in ionized gas tracers outside the globule, tracing the overall morphology of a jet-driven molecular outflow. Continuum emission at the location of the HH 900 YSO appears to be slightly flattened perpendicular to outflow axis. Model fits to the continuum have a best-fitting spectral index of ∼2, suggesting cold dust and the onset of grain growth. In position–velocity space, 13CO and C18O gas kinematics trace a C-shaped morphology, similar to infall profiles seen in other sources, although the global dynamical behaviour of the gas remains unclear. Line profiles of the CO isotopologues display features consistent with externally heated gas. We estimate a globule mass of ∼1.9 M⊙, indicating a remaining lifetime of ∼4 Myr, assuming a constant photoevaporation rate. This long globule lifetime will shield the disc from external irradiation perhaps prolonging its life and enabling planet formation in regions where discs are typically rapidly destroyed.
...Carinae, the most extreme luminous blue variable in our Galaxy, underwent a Great Eruption in the 1800s and ejected significant mass into the well-known bipolar Homunculus. But...Car's outer ...ejecta, a spread of dense, nitrogen-rich knots outside the Homunculus, have led to suspicion that the Great Eruption was not this star's first major mass-loss event. We have measured proper motions for nearly 800 distinct features in the outer ejecta using 21 years of HST WFPC2 and ACS imaging. With motions measured across sixteen baselines, we find that the outer ejecta are expanding ballistically and belong to three age groups: one dating to the mid-1200s, another to the mid-1500s, and a third to the early 1800s, associated with but perhaps predating the peak of the Great Eruption. These three age groups are separated in space and radial velocity. There is no evidence for interaction between the dense ejecta that could be powering...Car's soft X-ray shell, which is instead likely driven by fast, rarefied ejecta from the Great Eruption striking the older dense ejecta. The thirteenth-century event was strikingly asymmetric, ejecting mass almost entirely to one side of the star. The sixteenth-century event displays bipolar symmetry, but along a different axis than the current Homunculus. These observations provide constraints on theoretical models of...Car's behavior, as viable models must explain the repetition, timescale, and asymmetry of these major mass-loss events. For more details, see Kiminki, Reiter, & Smith (2016, MNRAS, 463, 845).
η Carinae, the most extreme luminous blue variable in our Galaxy, underwent a Great Eruption in the 1800s and ejected significant mass into the well-known bipolar Homunculus. But η Car's outer ...ejecta, a spread of dense, nitrogen-rich knots outside the Homunculus, have led to suspicion that the Great Eruption was not this star's first major mass-loss event. We have measured proper motions for nearly 800 distinct features in the outer ejecta using 21 years of HST WFPC2 and ACS imaging. With motions measured across sixteen baselines, we find that the outer ejecta are expanding ballistically and belong to three age groups: one dating to the mid-1200s, another to the mid-1500s, and a third to the early 1800s, associated with but perhaps predating the peak of the Great Eruption. These three age groups are separated in space and radial velocity. There is no evidence for interaction between the dense ejecta that could be powering η Car's soft X-ray shell, which is instead likely driven by fast, rarefied ejecta from the Great Eruption striking the older dense ejecta. The thirteenth-century event was strikingly asymmetric, ejecting mass almost entirely to one side of the star. The sixteenth-century event displays bipolar symmetry, but along a different axis than the current Homunculus. These observations provide constraints on theoretical models of η Car's behavior, as viable models must explain the repetition, timescale, and asymmetry of these major mass-loss events. For more details, see Kiminki, Reiter, & Smith (2016, MNRAS, 463, 845).
Recent work suggests that \(^{26}\)Al may determine the water budget in terrestrial exoplanets as its radioactive decay dehydrates planetesimals leading to rockier compositions. Here I consider the ...observed distribution of \(^{26}\)Al in the Galaxy and typical star-forming environments to estimate the likelihood of \(^{26}\)Al enrichment during planet formation. I do not assume Solar-System-specific constraints as I am interested in enrichment for exoplanets generally. Observations indicate that high-mass stars dominate the production of \(^{26}\)Al with nearly equal contributions from their winds and supernovae. \(^{26}\)Al abundances are comparable to those in the early Solar System in the high-mass star-forming regions where most stars (and thereby most planets) form. These high abundances appear to be maintained for a few Myr, much longer than the 0.7 Myr half-life. Observed bulk \(^{26}\)Al velocities are an order of magnitude slower than expected from winds and supernovae. These observations are at odds with typical model assumptions that \(^{26}\)Al is provided instantaneously by high velocity mass loss from supernovae and winds. Regular replenishment of \(^{26}\)Al especially when coupled with the small age differences that are common in high-mass star-forming complexes, may significantly increase the number of star/planet-forming systems exposed to \(^{26}\)Al. Exposure does not imply enrichment, but the order of magnitude slower velocity of \(^{26}\)Al may alter the fraction that is incorporated into planet-forming material. Together, this suggests that the conditions for rocky planet formation are not rare, nor are they ubiquitous, as small regions like Taurus that lack high-mass stars to produce \(^{26}\)Al may be less likely to form rocky planets. I conclude with suggested directions for future studies.
We present an analysis of the relation between the star formation rate (SFR) and mass of dense gas in Galactic clumps and nearby galaxies. Using the bolometric luminosity as a measure of SFR and the ...molecular line luminosity of HCO+ (3-2) as a measure of dense gas mass, we find that the relation between SFR and M dense is approximately linear. This is similar to published results derived using HCN (1-0) as a dense gas tracer. HCO+ (3-2) and HCN (1-0) have similar conditions for excitation. Our work includes 16 Galactic clumps that are in both the Bolocam Galactic Plane Survey and the Red MSX Source Survey, 27 water maser sources from the literature, and the aforementioned HCN (1-0) data. Our results agree qualitatively with predictions of recent theoretical models which state that the nature of the relation should depend on how the critical density of the tracer compares with the mean density of the gas.
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![Proper Motions of[...]Carin...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1743-9213/small "Proper Motions of[...]Carinae's Outer Ejecta and Its Eruptive History")
