The Coldest Place in the Universe: Probing the Ultra-Cold Outflow and Dusty Disk in the Boomerang Nebula

Our Cycle 0 ALMA observations confirmed that the Boomerang Nebula is the coldest known object in the Universe, with a massive high-speed outflow that has cooled significantly below the cosmic background temperature. Our new CO 1-0 data reveal heretofore unseen distant regions of this ultra-cold outflow, out to $\gtrsim120,000$ AU. We find that in the ultra-cold outflow, the mass-loss rate (dM/dt) increases with radius, similar to its expansion velocity ($V$) - taking $V\propto r$, we find $dM/dt \propto r^{0.9-2.2}$. The mass in the ultra-cold outflow is $\gtrsim3.3$ Msun, and the Boomerang's main-sequence progenitor mass is $\gtrsim4$ Msun. Our high angular resolution ($\sim$0".3) CO J=3-2 map shows the inner bipolar nebula's precise, highly-collimated shape, and a dense central waist of size (FWHM) $\sim$1740 AU$\times275$ AU. The molecular gas and the dust as seen in scattered light via optical HST imaging show a detailed correspondence. The waist shows a compact core in thermal dust emission at 0.87-3.3 mm, which harbors $(4-7)\times10^{-4}$ Msun~of very large ($\sim$mm-to-cm sized), cold ($\sim20-30$ K) grains. The central waist (assuming its outer regions to be expanding) and fast bipolar outflow have expansion ages of $\lesssim1925$ yr and $\le1050$ yr: the "jet-lag" (i.e., torus age minus the fast-outflow age) in the Boomerang supports models in which the primary star interacts directly with a binary companion. We argue that this interaction resulted in a common-envelope configuration while the Boomerang's primary was an RGB or early-AGB star, with the companion finally merging into the primary's core, and ejecting the primary's envelope that now forms the ultra-cold outflow.Comment: accepted ApJ, 12 Apr, 201

Pinpointing the Position of the Post-AGB Star at the Core of RAFGL 2688 using Polarimetric Imaging with NICMOS

We have used infrared polarimetric imaging with NICMOS to determine precisely the position of the star that illuminates (and presumably generated) the bipolar, pre-planetary reflection nebula RAFGL 2688 (the Egg Nebula). The polarimetric data pinpoint the illuminating star, which is not detected directly at wavelengths less than or equal to 2 microns, at a position well within the dark lane that bisects the nebula, 0.55" (about 550 AU) southwest of the infrared peak which was previously detected at the southern tip of the northern polar lobe. The inferred position of the central star corresponds to the geometric center of the tips of the four principle lobes of near-infrared H2 emission; identifying the central star at this position also reveals the strong point symmetric structure of the nebula, as seen both in the intensity and polarization structure of the polar lobes. The polarimetric and imaging data indicate that the infrared peak directly detected in the NICMOS images is a self-luminous source and, therefore, is most likely a distant binary companion to the illuminating star. Although present theory predicts that bipolar structure in pre-planetary and planetary nebulae is a consequence of binary star evolution, the separation between the components of the RAFGL 2688 binary system, as deduced from these observations, is much too large for the presence of the infrared companion to have influenced the structure of the RAFGL 2688 nebula.Comment: 15 pages, 6 figures, to appear in The Astrophysical Journa

Spitzer IRS Spectra of Luminous 8 micron Sources in the Large Magellanic Cloud: Testing color-based classifications

We present archival Spitzer IRS spectra of 19 luminous 8 micron selected sources in the Large Magellanic Cloud (LMC). The object classes derived from these spectra and from an additional 24 spectra in the literature are compared with classifications based on 2MASS/MSX (J, H, K, and 8 micron) colors in order to test the "JHK8" classification scheme (Kastner et al. 2008). The IRS spectra confirm the classifications of 22 of the 31 sources that can be classified under the JHK8 system. The spectroscopic classification of 12 objects that were unclassifiable in the JHK8 scheme allow us to characterize regions of the color-color diagrams that previously lacked spectroscopic verification, enabling refinements to the JHK8 classification system. The results of these new classifications are consistent with previous results concerning the identification of the most infrared-luminous objects in the LMC. In particular, while the IRS spectra reveal several new examples of asymptotic giant branch (AGB) stars with O-rich envelopes, such objects are still far outnumbered by carbon stars (C-rich AGB stars). We show that Spitzer IRAC/MIPS color-color diagrams provide improved discrimination between red supergiants and oxygen-rich and carbon-rich asymptotic giant branch stars relative to those based on 2MASS/MSX colors. These diagrams will enable the most luminous IR sources in Local Group galaxies to be classified with high confidence based on their Spitzer colors. Such characterizations of stellar populations will continue to be possible during Spitzer's warm mission, through the use of IRAC [3.6]-[4.5] and 2MASS colors.Comment: 31 pages, 10 figures, to be published in A

X-Ray Emission from the Pre-Planetary Nebula Henize 3-1475

We report the first detection of X-ray emission in a pre-planetary nebula, Hen 3-1475. Pre-planetary nebulae are rare objects in the short transition stage between the Asymptotic Giant Branch and planetary nebula evolutionary phases, and Hen 3-1475, characterised by a remarkable S-shaped chain of optical knots, is one of the most noteworthy members of this class. Observations with the Advanced CCD Imaging Spectrometer (ACIS) onboard the Chandra X-Ray observatory show the presence of compact emission coincident with the brightest optical knot in this bipolar object, which is displaced from the central star by 2.7 arcsec along the polar axis. Model fits to the X-ray spectrum indicate an X-ray temperature and luminosity, respectively, of (4.3-5.7) 10^6 K and (4+/-1.4) 10^{31} (D/5 kpc)^2 erg s^{-1}, respectively. Our 3-sigma upper limit on the luminosity of compact X-ray emission from the central star in Hen 3-1475 is ~5 10^{31} (D/5 kpc)^2 erg s^{-1}. The detection of X-rays in Hen 3-1475 is consistent with models in which fast collimated post-AGB outflows are crucial to the shaping of planetary nebulae; we discuss such models in the context of our observations.Comment: 2 figure

The enigmatic B[e]-star Henize 2-90: The non-spherical mass loss history from an analysis of forbidden lines

(abridged) We study the optical spectrum of the exciting B[e] star Hen 2-90 based on new high-resolution observations that cover the innermost 2". Our investigation is splitted in two parts, a qualitative study of the presence of the numerous emission lines and the classification of their line profiles which indicate a circumstellar environment of high complexity, and a quantitative analysis of numerous forbidden lines, e.g. [OI], [OII], [OIII], [SII], [SIII], [ArIII], [ClII], [ClIII] and [NII]. We find a correlation between the different ionization states of the elements and the velocities derived from the line profiles: the highly ionized atoms have the highest outflow velocity while the neutral lines have the lowest outflow velocity. The recent HST image of Hen 2-90 reveals a bipolar, highly ionized region, a neutral disk-like structure and an intermediate region of moderate ionization. It seems that a non-spherical stellar wind model is a good option to explain the ionization and spatial distribution of the circumstellar material. We modelled the forbidden lines under the assumption of a non-spherically symmetric wind based on the HST image. We find that in order to fit the observed line luminosities, the mass flux, surface temperature, and terminal wind velocities need to be latitude dependent, which might be explained in terms of a rapidly rotating central star. A rotation speed of 75-80 % of the critical velocity has been derived. The total mass loss rate of the star was determined to be of order 3 10^{-5} M_sun/yr. Such a wind scenario and the fact that compared to solar abundances C, O, and N seem to be underabundant while S, Ar and Cl have solar abundances, might be explained in terms of a rapidly rotating post-AGB star.Comment: 16 pages, 13 figures, accepted for publication in A&A. Table 4 is included at the end of the paper. This table will only be available in the online version of the paper and will not appear in the printed versio

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

The kinematics of water masers in the stellar molecular outflow source IRAS 19134+2131

Using the Very Large Array (VLA) and the Very Long Baseline Array (VLBA), we have observed water maser emission in the proto-planetary nebula candidate IRAS 19134+2131, in which the water maser spectrum has two groups of emission features separated in radial velocity by ∼100 km s^−1. The blue-shifted and red-shifted clusters of maser features are clearly separated spatially by ∼150 mas, indicative of a fast collimated flow. However, not all of the maser features are aligned along the axis of the flow, as is seen in the similar high-velocity water maser source, W43A. Comparing the VLA and VLBA maps of the water maser source, we find 4 maser features that were active for 2 years. Using only VLBA data, we identified proper motions for 8 maser features. The full 3D outflow velocity is estimated to be ∼130 km s^−1, indicating that the dynamical age of the flow is only ∼50 yr. On the basis of the relative positions with respect to the nearby extragalactic reference source, J1925+2106, we also obtain a secular motion of IRAS 19134+2131 of μl = −4.6 ± 0.7 mas yr^−1 along the Galactic plane toward the Galactic centre. This indicates a “far distance” (≥16 kpc) for IRAS 19134+2131 if the Galactic rotation curve remains flat at 220 km s^−1.Hachisuka, Kazuya, [email protected]

X-ray emission from Planetary Nebulae. I. Spherically symmetric numerical simulations

(abridged) The interaction of a fast wind with a spherical Asymptotic Giant Branch (AGB) wind is thought to be the basic mechanism for shaping Pre-Planetary Nebulae (PPN) and later Planetary Nebulae (PN). Due to the large speed of the fast wind, one expects extended X-ray emission from these objects, but X-ray emission has only been detected in a small fraction of PNs and only in one PPN. Using numerical simulations we investigate the constraints that can be set on the physical properties of the fast wind (speed, mass-flux, opening angle) in order to produce the observed X-ray emission properties of PPNs and PNs. We combine numerical hydrodynamical simulations including radiative cooling using the code FLASH with calculations of the X-ray properties of the resulting expanding hot bubble using the atomic database ATOMDB. In this first study, we compute X-ray fluxes and spectra using one-dimensional models. Comparing our results with analytical solutions, we find some agreements and many disagreements. In particular, we test the effect of different time histories of the fast wind on the X-ray emission and find that it is determined by the final stage of the time history during which the fast wind velocity has its largest value. The disagreements which are both qualitative and quantitative in nature argue for the necessity of using numerical simulations for understanding the X-ray properties of PNs.Comment: 17 pages, accepted for publication in ApJ (July 27, 2006), uses emulateap