Optical Reflection Nebula Research Articles

The ALMA early science view of FUor/EXor objects – IV. Misaligned outflows in the complex star-forming environment of V1647 Ori and McNeil's Nebula

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor pre-MS star. Dust continuum and the (J = 2 - 1) $^{12}$CO, $^{13}$CO, C$^{18}$O molecular emission lines were observed to characterize the V1647 Ori circumstellar disc and any large scale molecular features present. We detect continuum emission from the circumstellar disc and determine a radius r = 40 au, inclination i = 17$^{\circ}$$^{+6}_{-9}$ and total disc mass of M$_{\mathrm{disk}}$ of ~0.1 M$_{\odot}$. We do not identify any disc structures associated with nearby companions, massive planets or fragmentation. The molecular cloud environment surrounding V1647 Ori is both structured and complex. We confirm the presence of an excavated cavity north of V1647 Ori and have identified dense material at the base of the optical reflection nebula (McNeil's Nebula) that is actively shaping its surrounding environment. Two distinct outflows have been detected with dynamical ages of ~11,700 and 17,200 years. These outflows are misaligned suggesting disc precession over ~5500 years as a result of anisotropic accretion events is responsible. The collimated outflows exhibit velocities of ~2 km s$^{-1}$, similar in velocity to that of other FUor objects presented in this series but significantly slower than previous observations and model predictions. The V1647 Ori system is seemingly connected by an "arm" of material to a large unresolved structure located ~20$"$ to the west. The complex environment surrounding V1647 Ori suggests it is in the early stages of star formation which may relate to its classification as both an FUor and EXor type object.

INTERACTIONS BETWEEN FORMING STARS AND DENSE GAS IN THE SMALL LOW-MASS CLUSTER CEDERBLAD 110

We present observations of dense gas and outflow activity in the Cederblad 110 region of the Chamaeleon I dark cloud complex. The region contains nine forming low-mass stars in evolutionary stages ranging from Class 0 to Class II/III crowded into a 0.2 pc region with high surface density ({Sigma}{sub YSO} {approx} 150 pc{sup -2}). The analysis of our N{sub 2}H{sup +} (J = 1{yields}0) maps indicates the presence of 13 {+-} 3 solar masses of dense (n {approx} 10{sup 5} cm{sup -3}) gas in this region, much of which is unstable against gravitational collapse. The most unstable material is located near the Class 0 source MMS-1, which is almost certainly actively accreting material from its dense core. Smaller column densities of more stable dense gas are found toward the region's Class I sources, IRS 4, 11, and 6. Little or no dense gas is colocated with the Class II and III sources in the region. The outflow from IRS 4 is interacting with the dense core associated with MMS-1. The molecular component of the outflow, measured in the (J = 1{yields}0) line of {sup 12}CO, appears to be deflected by the densest part of the core, after which it appearsmore » to plow through some of the lower column density portions of the core. The working surface between the head of the outflow lobe and the dense core material can be seen in the enhanced velocity dispersion of the dense gas. IRS 2, the Class III source that produces the optical reflection nebula that gives the Cederblad 110 region its name, may also be influencing the dense gas in the region. A dust temperature gradient across the MMS-1 dense core is consistent with warming from IRS 2, and a sharp gradient in dense gas column density may be caused by winds from this source. Taken together, our data indicate that this region has been producing several young stars in the recent past, and that sources which began forming first are interacting with the remaining dense gas in the region, thereby influencing current and future star formation activity.« less

Millimeter interferometric observations of FU Orionis-type objects in Cygnus

FU Orionis-type objects (FUors) are low-mass young eruptive stars that represent an evolutionary phase characterized by episodic periods of increased accretion rate from the disk to the star. Theory predicts that a circumstellar envelope, the source of continuous mass infall onto the disk, is necessary for triggering such accretion bursts. We study the spatial and velocity structure of envelopes around FUors by means of molecular line observations at mm wavelengths. We target three prototypical FUors and an object possibly in a pre-outburst state. We present archival PdBI interferometric observations of the J=1-0 line of 13CO at 110.2 GHz. For three of our targets, these represent the first mm interferometric observations. The data allow the study of the molecular environment of the objects on a spatial resolution of a thousand AU and a velocity resolution of 0.2 km/s. Strong, narrow 13CO(1-0) line emission is detected from all sources. The emission is spatially resolved in all cases, with deconvolved sizes of a few thousand AUs. For V1057 Cyg and V1331 Cyg, the emitting area is rather compact, suggesting that the origin of emission is an envelope surrounding the central star. For V1735 Cyg, the 13CO emission is offset from the stellar position, indicating that the source of emission may be a small foreground cloud, also responsible for the high reddening of the central star. The 13CO emission towards V1515 Cyg is the most extended in the sample, and coincides with the ring-like optical reflection nebula associated with V1515 Cyg. We suggest that mm interferometric observations are indispensable for a complete understanding of the circumstellar environment of FUors. Any theory of the FUor phenomenon that interprets the geometry of the circumstellar structure and its evolution using single beam measurements must be checked and compared to interferometric observations in the future.

Young stars and reflection nebulae near the lower “edge” of the Galactic molecular disc

<i>Aims. <i/>We investigate the star formation occurring in a region well below the Galactic plane towards the optical reflection nebula ESO 368-8 (IRAS 07383-3325). We confirm the presence of a small young stellar cluster (or aggregate of tens of YSOs) identified earlier, embedded in a molecular cloud located near the lower “edge” of the Galactic disc, and characterise the young stellar population. We report the discovery of a near-infrared nebula, and present a CO map revealing a new dense, dynamic cloud core.<i>Methods. <i/>We used near-infrared images obtained with VLT/ISAAC, millimetre CO spectra obtained with the SEST telescope, and optical <i>V<i/>-band images from the YALO telescope.<i>Results. <i/>This star formation region displays an optical reflection nebula (ESO 368-8) and a near-infrared nebula located about 46<i>''<i/> (1.1 pc) from each other. The two nebulae are likely to be coeval and to represent two manifestations of the same single star formation episode with about 1 Myr age. The near-IR nebula reveals an embedded, optically and near-IR invisible source whose light scatters off a cavity carved by previous stellar jets or molecular outflows and into our line-of-sight. The molecular cloud is fully covered by our CO(<i>J<i/> = 1-0) maps and, traced by this line, extends over a region of <i>7.8<i/> pc<sup>2<sup/>, exhibiting an angular size <i>5.4'<i/> and shape (close to circular) similar to spherical (or slightly cometary) globules. Towards the direction of the near-IR nebula, the molecular cloud contains a dense core where the molecular gas exhibits large line widths indicative of a very dynamical state, with stirred gas and supersonic motions. Our estimates of the mass of the molecular gas in this region range from 600 to 1600 . The extinction <i>A<sub>V<sub/><i/> towards the positions of the optical reflection nebula and of the near-IR nebula was found to be mag and mag, respectively.

Young Stellar Objects in G[CLC]y[/CLC] 2-18 (IRAS 05439+3035)

We present the results of optical and near-IR spectra and mid-infrared images of the star forming region Gy 2-18, which is associated with IRAS 05439+3035. Within this region, there is a star with strong Hα emission that is illuminating an optical reflection nebula. Optical and near-IR spectra indicate that this star, named IRS 11, is a possible Herbig Be star of spectral type BO–B2, with a strong stellar wind and an infrared excess probably originating in a circumstellar dust disk. The mid-infrared images at 8.7, 9.7, and 12.5 μm show the presence of a second very red source, IRS 9, deeply embedded in the cloud and with a remarkably strong silicate feature in absorption. The estimated bolometric luminosity of 8.6 × 103 L⊙ and the infrared spectral index αIR = 1.9 suggest that IRS 9 is a massive protostellar object. These two sources form the core of the young stellar cluster associated with Gy 2-18. The infrared luminosity and spectral index of another member, IRS 13, are estimated to be ≤165 L⊙ and ≤0.44.

Near-infrared discovery of the L810 nebula illuminator

view Abstract Citations (16) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Discovery of the L810 Nebula Illuminator Yun, Joao L. ; Clemens, Dan P. ; McCaughrean, Mark J. ; Rieke, Marcia Abstract As part of a deep NIR imaging survey for IR point sources in Bok globules, we have discovered the illuminator of the optical reflection nebula seen toward the Bok globule L810. The illuminator (L810 IRS) is located at the position predicted by Scarrott et al. (1991) from analysis of their optical polarimetry. This source is very red (J-K about 3.9) and bright (mK = 10.7), and has an estimated bolometric luminosity of 890 solar luminosities. A NIR nebula was found which extends 20 arcsec symmetrically to the north and to the south of L810 IRS, exhibiting an hourglass shape. Both the morphology and the orientation of the NIR nebula are in good agreement with the morphology and orientation of the high-velocity molecular outflow associated with L810. Finally, we found a NIR jetlike structure whose axis is collinear with L810 IRS. Together, these findings indicate that L810 IRS is likely to be a deeply embedded, very active intermediate-mass young stellar object within the L810 cloud. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/186841 Bibcode: 1993ApJ...408L.101Y Keywords: Infrared Imagery; Infrared Stars; Interstellar Matter; Point Sources; Reflection Nebulae; Star Formation; Infrared Astronomy; Near Infrared Radiation; Astrophysics; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE; ISM: INDIVIDUAL ALPHANUMERIC: L810; ISM: JETS AND OUTFLOWS; ISM: REFLECTION NEBULAE; INFRARED: STARS full text sources ADS | data products SIMBAD (3)

CO Interferometric Maps of CIT 6 and CRL 618

We present CO (1−0) interferometer maps of carbon star, CIT 6, and carbon rich proto-planetary nebula, CRL618. Both objects were mapped with the Berekeley-Illinois-Maryland millimeter array (BIMA). The resulting resolution is ∼ 4″ and structure larger than ∼1′ is completely filtered out. Two velocity resolutions were employed; 0.4 km s−1 and 0.8 km s−1 permitting a velocity coverage of 52 and 104 km s−1. We find evidence for non-spherical expanding envelopes in both objects. The interferometer detected all the single dish CO flux in CRL618 (840 Jy km s−1), and 70% of the CO flux in CIT 6 (or 1030 Jy km s−1). For CIT 6, we obtained single dish maps at the NRAO 12m to measure the zero spacing flux distribution. We measure an envelope diameter of 90″ (2.6 × 1017 at 190 pc) for CIT 6 and 15″ (4.5 × 1017 at 2 kpc) for CRL 618 and expansion velocities of 17 km s−1 for both. The small scale structure seen by the interferometer in CIT 6 has a core and an elongation to the SW. We interpret this elongation as the beginning of an equatorial density enhancement and predict that that CIT 6 will evolve into a bipolar planetary nebula. In CRL 618, the elongated structure seen in CO is perpendicular to the optical reflection nebula, which has an east-west orientation. Hence the Asymptotic Giant Branch (AGB) wind appears as an expanding waist band around this bipolar nebula giving credence to the idea that equatorial density enhancements in AGB winds produce bipolar planetary nebulae (Balick 1987).

C II 158 micron and O I 63 micron observations of NGC 7023 - A model for its photodissociation region

Emission in the far IR fine-structure lines of O I (63 microns) and C II (158 microns) from the bright optical reflection nebula NGC 7023 has been observed. It is suggested that this emission arises in a warm, atomic photodissociation region produced by the interaction of the UV radiation of the illuminating star with a molecular cloud. The density and temperature in the photodissociation region is estimated and a model for the region is constructed.

Aperture-synthesis observations of carbon monoxide in the EGG Nebula

The authors have mapped the λ = 2.6 mm emission from CO in the bipolar nebula CRL 2688 (the Egg Nebula) with 7arcsec resolution using the Owens Valley millimeter-wave interferometer. The detected CO emission is confined to a bright core 10arcsec×15arcsec in size; it is centered on and has the same position angle as the optical reflection nebula. There is a velocity gradient of 3 km s<SUP>-1</SUP>arcsec<SUP>-1</SUP> along the major axis of the core source. The bright core source has a high excitation temperature of ≡70K. The similarity between the CO and optical images strongly suggests that the bright CO core is spatially coincident with the visible reflecting dust.