Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpatial distribution and kinematics of the molecular material associated with $eta$ Carinae
92
0
0.0
(
0
)
Authors
L. Loinard
Ask ChatGPT about the research
No Arabic abstract
Single-dish sub-millimeter observations have recently revealed the existence of a substantial, chemically peculiar, molecular gas component located in the innermost circumstellar environment of the very massive luminous blue variable star $eta$ Carinae. Here, we present 5$$-resolution interferometric observations of the 1$rightarrow$0 rotational transition of hydrogen cyanide (HCN) obtained with the Australia Telescope Compact Array (ATCA) toward this star. The emission is concentrated in the central few arcseconds around $eta$ Carinae and shows a clear 150 km s$^{-1}$ velocity gradient running from west-north-west (blue) to east-south-east (red). Given the extent, location, and kinematics of this molecular material, we associate it with the complex of dusty arcs and knots seen in mid-infrared emission near the center of the Homunculus nebula. Indeed, the shielding provided by this dust could help explain how molecules survive in the presence of the intense UV radiation field produced by $eta$ Carinae. The dust located in the central few arcseconds around $eta$ Carinae and the molecular component described here have most likely formed in situ, out of material expelled by the massive interacting binary system. Thus, $eta$ Carinae offers us a rare glimpse on the processes leading to the formation of dust and molecules around massive stars that are so relevant to the interpretation of dust and molecule detections at high redshifts.
rate research
Read More
We present a high-resolution image of $eta$~Car. Together with IR and visual observations of the central arcsecond, we use this to discuss the morphological structure of $eta$~Car on the different length scales. We identify three different structural components: a bipolar outflow, an equatorial disk of streamers, and the speckle objects. We discuss models for the kinematics of the whole complex, and propose observations that could settle the question of the structure of $eta$~Car.
In circumstellar gas, the complex organic molecule methanol has been found almost exclusively around young stellar objects, and is thus regarded as a signpost of recent star formation. Here we report the first probable detection of methanol around an evolved high-mass star, in the complex circumstellar environment around the Luminous Blue Variable $eta$ Carinae, while using ALMA to investigate molecular cloud conditions traced by CO (2-1) in an orbit phase of the massive binary preceding the 2020 periastron. Favoring methanol over a $^{13}$CS alternative, the emission originates from hot ($T_{rm{gas}} simeq$ 700 K) material, $sim$2$$ (0.02 pc) across, centered on the dust-obscured binary in contrast to the CO which traces inner layers of the extended massive equatorial torus, and is accompanied by prominent absorption in a cooler ($T_{rm{gas}} simeq$ 110 K) layer of gas. We also report detections of water in $Herschel$/HIFI observations at 557 GHz and 988 GHz. The methanol abundance is several to 50 times higher than observed towards several lower mass stars, while water abundances are similar to those observed in cool, dense molecular clouds. The very high methanol:water abundance ratio in the core of $eta$ Carinae may suggest methanol formation processes similar to Fischer-Tropsch-type catalytic reactions on dust grains. These observations prove that complex molecule formation can occur in the chemically evolved environments around massive stars in the end stages of their evolution, given sufficient gas densities and shielding conditions as may occur in material around massive interacting companions and merger remnants.
During the years 1838-1858, the very massive star {eta} Carinae became the prototype supernova impostor: it released nearly as much light as a supernova explosion and shed an impressive amount of mass, but survived as a star.1 Based on a light-echo spectrum of that event, Rest et al.2 conclude that a new physical mechanism is required to explain it, because the gas outflow appears cooler than theoretical expectations. Here we note that (1) theory predicted a substantially lower temperature than they quoted, and (2) their inferred observational value is quite uncertain. Therefore, analyses so far do not reveal any significant contradiction between the observed spectrum and most previous discussions of the Great Eruption and its physics.
We present Atacama Large Millimeter Array (ALMA) observations of $^{12}$CO2$-$1 emission from circumstellar material around the massive star $eta$~Carinae. These observations reveal new structural details about the cool equatorial torus located $sim$4000 au from the star. The CO torus is not a complete azimuthal loop, but rather, is missing its near side, which appears to have been cleared away. The missing material matches the direction of apastron in the eccentric binary system, making it likely that $eta$~Cars companion played an important role in disrupting portions of the torus soon after ejection. Molecular gas seen in ALMA data aligns well with the cool dust around $eta$~Car previously observed in mid-infrared (IR) maps, whereas hot dust resides at the inner surface of the molecular torus. The CO also coincides with the spatial and velocity structure of near-IR H$_2$ emission. Together, these suggest that the CO torus seen by ALMA is actually the pinched waist of the Homunculus polar lobes, which glows brightly because it is close to the star and warmer than the poles. The near side of the torus appears to be a blowout, associated with fragmented equatorial ejecta. We discuss implications for the origin of various features northwest of the star. CO emission from the main torus implies a total gas mass in the range of 0.2-1 $M_{odot}$ (possibly up to 5 $M_{odot}$ or more, although with questionable assumptions). Deeper observations are needed to constrain CO emission from the cool polar lobes.
We present images of $eta$ Carinae in the recombination lines H30$alpha$ and He30$alpha$ and the underlying continuum with 50~mas resolution (110 AU), obtained with ALMA. For the first time, the 230 GHz continuum image is resolved into a compact core, coincident with the binary system position, and a weaker extended structure to the NW of the compact source. Iso-velocity images of the H30$alpha$ recombination line show at least 16 unresolved sources with velocities between -30 and -65 km s$^{-1}$ distributed within the continuum source. A NLTE model, with density and temperature of the order $10^7$ cm$^{-3}$ and $10^4$ K, reproduce both the observed H30$alpha$ line profiles and their underlying continuum flux densities. Three of these sources are identified with Weigelt blobs D, C and B; estimating their proper motions, we derive ejection times (in years) of 1952.6, 1957.1, and 1967.6, respectively, all of which are close to periastron passage. Weaker H30$alpha$ line emission is detected at higher positive and negative velocities, extending in the direction of the Homunculus axis. The He30$alpha$ recombination line is also detected with the same velocity of the narrow H30$alpha$ line. Finally, the close resemblance of the H30$alpha$ image with that of an emission line that was reported in the literature as HCO$^+$(4-3) led us to identify this line as H40$delta$ instead, an identification that is further supported by modeling results. Future observations will enable to determine the proper motions of all the compact sources discovered in the new high-angular resolution data of $eta$ Carinae.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
