A Study of the Cometary Globules in the GUM Nebula

2022

Context. The ultraviolet irradiation and the action of stellar winds of newly formed massive stars on their parental molecular environment often produces isolated or small clouds, some of which become sites of star formation themselves. Aims. We investigate the young stellar populations associated with DR 18 and ECX 6-21, which are two isolated globules irradiated by the O-type stars of the Cygnus OB2 association. Both are HII regions containing obvious tracers of recent and ongoing star formation. We also study smaller isolated molecular structures in their surroundings. Methods. We combined near-infrared broad-and narrow-band imaging with broad-band imaging in the visible and with archive images obtained with the Spitzer Space Telescope. We used the joint photometry to select young stellar objects (YSOs), simultaneously estimating their intrinsic properties and classifying them according to the characteristics of their infrared excess. We also present low-resolution visible spectroscopy of selected sources. Results. We reproduce previous findings of an extended population of YSOs around both globules, dominated by the more evolved classes, associated with the general Cygnus OB2 population. Both globules contain their own embedded populations, with a higher fraction of the less-evolved classes. Masses and temperatures are estimated under the assumption of a common age of 1 Myr, which has been found to appropriately represent the general Cygnus OB2 YSO population but is most probably an overestimate for both globules, especially ECX 6-21. The early-B star responsible for the erosion of DR 18 is found to be part of a small aggregate of intermediatemass stars still embedded in the cloud, which probably contains a second site of recent star formation, also with intermediate-mass stars. We confirm the two main star forming sites embedded in ECX 6-21 described in previous works, with the southern site being more evolved than the northern site. We also discuss the small globule ECX 6-21-W (= G79.8 + 1.2), and propose that its non thermal radio spectrum is due to synchrotron emission from an embedded jet, whose existence is suggested by our observations. Conclusions. The extreme youth of some of the YSOs suggests that star formation in both globules started after they became externally irradiated. The populations of both globules are not found to be particularly rich, but they contain stars with estimated masses similar or above that of the Sun in numbers that hint at some differences with respect to the star formation process taking place in more quiescent regions where low-mass stars dominate, which deeper observations may confirm.

Monthly Notices of the Royal Astronomical Society, 2000

We report the first results of imaging the Carina Nebula (NGC 3372) with the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope, providing a photometry catalog of over 44,000 point sources as well as a catalog of over 900 candidate young stellar objects (YSOs) based on fits to their spectral energy distributions (SEDs). We discuss several aspects of the extended emission, including the structure of dozens of dust pillars that result when a clumpy molecular cloud is shredded by feedback from massive stars. There are surprisingly few of the "extended green objects" (EGOs) that are normally taken as signposts of outflow activity in Spitzer data, and not one of the dozens of Herbig-Haro jets detected optically are seen as EGOs. EGOs are apparently poor tracers of outflow activity in strongly irradiated environments, due to the effects of massive star feedback. A population of "extended red objects" tends to be found around late O-type and early B-type stars, some with clear bow-shock morphology. These are dusty shocks where stellar winds collide with photoevaporative flows off nearby clouds. Finally, the relative distributions of O-type stars, small star clusters, and sub-clusters of YSOs as compared to the dust pillars shows that while some YSOs are located within dust pillars, many more stars and YSOs reside just outside pillar heads. We suggest that pillars are transient phenomena, part of a continuous outwardly propagating wave of star formation driven by feedback from massive stars. As the pillars are destroyed, they leave newly formed stars in their wake, and these are then subsumed into the young OB association. The YSOs are found predominantly in the cavity between pillars and massive stars, arguing that their formation was in fact triggered. Altogether, the current generation of YSOs shows no strong deviation from a normal initial mass function (IMF). The number of YSOs is consistent with a roughly constant star-formation rate over the past ∼3 Myr, implying that propagating star formation in pillars constitutes an important mechanism to construct unbound OB associations. These accelerated pillars may give birth to massive O-type stars that, after several Myr, could appear to have formed in isolation.

2002

Abstract. The kinematics and physical conditions of the bipolar planetary nebula M 2-48 are analysed from high and low dispersion long-slit spectra. Previous CCD narrow-band optical observations have suggested that this nebula is mainly formed by a pair of symmetric bowshocks, an off-center semi-circular shell, and an internal bipolar structure. The bipolar outflow has a complex structure, characterised by a series of shocked regions located between the bright core and the polar tips. There is an apparent kinematic discontinuity between the bright bipolar core and the outer regions. The fragmented ring around the bright bipolar region presents a low expansion velocity and could be associated to ejection in the AGB-PN transition phase, although its nature remains unclear. The chemical abundances of the central region are derived, showing that M 2-48 is a Type I planetary nebula (PN).

The Astrophysical Journal, 1998

We present new Hubble Space Telescope (HST ) Faint Object Spectrograph (FOS) and ground-based long-slit spectroscopic observations of the nebulae around the two LMC luminous blue variables (LBVs) R127 (\HDE 269858) and R143 (\HDE 269929) and the Ofpe/WN9 star S119 (\HDE 269687). We have used the ground-based long-slit spectra to investigate the kinematics of the nebulae around R127 and R143. We Ðnd that the circumstellar environment of R127 is complex and suggestive of two discrete ejections in the mass loss history of the central star. There is an inner expanding shell, with a radius of 0.6 pc, an expansion velocity of 29 km s~1, and a dynamical age of 2 ] 104 yr. There is also material beyond the bright inner nebula that may represent an outer expanding shell with a radius of 1.9 pc and a dynamical age of 7 ] 104 yr. For R143, we Ðnd that the velocity Ðeld in the northern and southern circumstellar regions (1AÈ20A) is predominantly constant. Therefore, the nebular emission previously believed to be associated with R143 (the Ðngers) is most likely part of the 30 Doradus complex, with the exception of a small emission-line region located^2A north of the star. This compact region displays a blueshifted motion with a di †erential velocity of^130 km s~1 with respect to the central star. The spectrum of this clump shows a high [N II]/Ha ratio, suggestive of nitrogen-enriched material that has been ejected from the star some 3.7 ] 103 yr ago.

Astronomy and Astrophysics, 2009

Aims. Expanding HII regions and propagating shocks are common in the environment of young high-mass star-forming complexes. They can compress a pre-existing molecular cloud and trigger the formation of dense cores. We investigate whether these phenomena can explain the formation of high-mass protostars within an infrared dark cloud located at the position of G327.3-0.6 in the Galactic plane, in between two large infrared bubbles and two HII regions. Methods. The region of G327.3-0.6 was imaged at 450 µm with the CEA P-ArTéMiS bolometer array on the Atacama Pathfinder EXperiment telescope in Chile. APEX/LABOCA and APEX-2A, and Spitzer/IRAC and MIPS archives data were used in this study. Results. Ten massive cores were detected in the P-ArTéMiS image, embedded within the infrared dark cloud seen in absorption at both 8 and 24 µm. Their luminosities and masses indicate that they form high-mass stars. The kinematical study of the region suggests that the infrared bubbles expand toward the infrared dark cloud.

We present m ulti-transition observations of the HCO + molecule toward the very young star forming region associated with the NGC 2264G molecular out ow. Anomalous emission is observed in the lowest rotational transition: the J=4!3 and J=3!2 transitions clearly trace the dense core encompassing the exciting source of the molecular out ow, whereas the HCO + J=1!0 is barely detected at a much l o wer intensity and has a much broader line shape. Analysis of the data strongly suggests that the HCO + J=1!0 emission arising from the core is being absorbed e ciently by a cold low density e n velope around the core or a foreground cloud. This result seems exceptional, yet the J=1!0 HCO + and HCN emission from other dense cores especially those in giant molecular clouds may be a ected. In these cases, the rare isotopes of these molecules and higher rotational transitions of the main isotopes should be used to study these regions. Two quiescent clumps, JMG99 G1 and G2, are detected in the blue lobe of the NGC 2264G molecular out ow, close to shock excited near-IR H 2 knots. These clumps belong to the class of radiatively excited clumps, i.e., the radiation from the shock e v aporates the dust mantles and initiates a photochemical process, enhancing the emission of the HCO + .

Arxiv preprint astro-ph/ …, 1998

Astronomy & Astrophysics, 2013

Context. The temperature and density structure of molecular cloud cores are the most important physical quantities that determine the course of the protostellar collapse and the properties of the stars they form. Nevertheless, density profiles often rely either on the simplifying assumption of isothermality or on observationally poorly constrained model temperature profiles. The instruments of the Herschel satellite provide us for the first time with both the spectral coverage and the spatial resolution that is needed to directly measure the dust temperature structure of nearby molecular cloud cores. Aims. With the aim of better constraining the initial physical conditions in molecular cloud cores at the onset of protostellar collapse, in particular of measuring their temperature structure, we initiated the Guaranteed Time Key Project (GTKP) "The Earliest Phases of Star Formation" (EPoS) with the Herschel satellite. This paper gives an overview of the low-mass sources in the EPoS project, the Herschel and complementary ground-based observations, our analysis method, and the initial results of the survey. Methods. We study the thermal dust emission of 12 previously well-characterized, isolated, nearby globules using FIR and submm continuum maps at up to eight wavelengths between 100 µm and 1.2 mm. Our sample contains both globules with starless cores and embedded protostars at different early evolutionary stages. The dust emission maps are used to extract spatially resolved SEDs, which are then fit independently with modified blackbody curves to obtain line-of-sight-averaged dust temperature and column density maps. Results. We find that the thermal structure of all globules (mean mass 7 M ) is dominated by external heating from the interstellar radiation field and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (8-12 K) with column densities of a few 10 22 cm −2 . The protostars embedded in some of the globules raise the local temperature of the dense cores only within radii out to about 5000 AU, but do not significantly affect the overall thermal balance of the globules. Five out of the six starless cores in the sample are gravitationally bound and approximately thermally stabilized. The starless core in CB 244 is found to be supercritical and is speculated to be on the verge of collapse. For the first time, we can now also include externally heated starless cores in the L smm / L bol vs. T bol diagram and find that T bol < 25 K seems to be a robust criterion to distinguish starless from protostellar cores, including those that only have an embedded very low-luminosity object.

Astrophysical Journal, 2002

We report sensitive ATCA radio continuum observations toward IRAS 15596−5301 and 16272−4837, two luminous objects (L > 2 × 10 4 L ⊙ ) thought to represent massive star forming regions in early stages of evolution (due to previously undetected radio emission at the 1σ level of 2 mJy per beam). Also reported are 1.2 millimeter continuum and a series of molecular line observations made with the SEST telescope.

RevMexAA (Serie de …, 2003

Que los chorros fuertes puedan lanzarse en las etapas muy tempranas de las nebulosas preplanetarias no tiene mejor evidencia que en la clase de "nebulosas fuente de agua": sistemas en los cuales los máseres de H 2 O de muy alta velocidad están ubicados a lo largo del eje polar. El miembro más extremo conocido de esta clase es IRAS 16342−3814 que tiene emisión de maser de H 2 O a velocidades radiales de ±160 km s −1 relativas a la velocidad sistémica central. Por lo tanto, esto impone las restricciones más fuertes sobre la regulación y cinemática de los chorros dirigidos desde los polos de tales sistemas. En este trabajo describimos esta clase de objeto y reportamos los primeros resultados de nuestro estudio de los máseres de agua en IRAS 16342 hecho con el VLBA. En este estudio, todavía en progreso, los movimientos propios de los máseres, junto con sus velocidades radiales, deben proporcionarnos una idea bastante completa de la evolución de la dinámica de los chorros.

Monthly Notices of the Royal Astronomical Society, 2010

Using data from large-scale surveys: 2MASS, GLIMPSE, MIPSGAL, VGPS, GRS, and IPHAS, we performed a multiwavelength study of the ISM in a region of about 20 × 20 towards the molecular cloud G35.2-0.74. Additionally, the Ap 2-1 nebula, that is seen in projection over the molecular cloud, was studied using optical data obtained with the 2.15 m telescope at CASLEO, Argentina. From the HI absorption study we estimate a distance of ∼ 2 kpc for Ap 2-1 confirming that the nebula is embedded in the south portion of the molecular cloud G35.2-0.74. Performing a photometric study and analysing the spectral energy distributions of the sources likely embedded in the cloud, we confirm that this region is very active in star formation, mainly towards the north, where we discover a cluster of young stellar objects. From the Hα and [NII] lines we obtain a radial velocity of v LSR ∼ 31 km s −1 for the Ap 2-1 nebula, in coincidence with the velocity of the molecular cloud. Finally, we conclude that Ap 2-1 is an HII region probably excited by an early B-type star.

The Astrophysical Journal, 1993

Wcprcscnt a study of newly idcl)tificd colllctaryglobulcs in the south-cast quadrant of the Rosette Nebula usiI1g the J==l-O transition of carboli monoxide. The globules arc found to be blue-shiftcxl by about 6 km s-' with respect to the adjacent Rosette Molecular Cloud. '1'hc masses of the globules vary from 50 to 300 A4@, and their sizes arc bctwccn 1 and 3 pc. Two of the globules have cometary morphology and show velocity gradients of ~ 1.5 km s-] pc-] along their symtnctry axes. These globules are associated with the IR.AS sources 06314+0421, X0632+043, 06322+0427 and 06327+0423 which coincide with local maxima in the 13C0 emission. '1'hc derived physical paramckrs of the glob-UICS arc found to bc consistent with those prcdictccl by rcccnt theoretical models of photocvaporating cometary clouds. We suggest that star formation incluccd by radiation driven implosion has occurred.

Astrochemistry of Cosmic Phenomena, 1992

Using high-resolution infrared CO spectroscopy new results have been obtained on the environment of high-mass young stellar objects (YSOs). In particular, a new class of neutral, warm and dense outflows has been discovered. The infrared outflows appear a general phenomenon of the activity of high-mass YSOs. With well-defined and often multiple velocities they seem to correspond to episodic and violent mass-loss events from the central source. In addition, a shell of warm, quiescent gas, is formed near the massive star. All these dynamical elements influence the chemistry inside the giant molecular clouds. Beside CO in solid and in gas phase, detection in the infrared has been attempted of simple molecules like CH4, C2H2, H2O and ion H^" toward few of these sources.

The Astrophysical Journal, 2012

We mapped the (1,1), (2,2), and (3,3) lines of NH 3 toward the molecular cloud associated with the Monkey Head Nebula (MHN) with a 1. 6 angular resolution using a Kashima 34 m telescope operated by the National Institute of Information and Communications Technology (NICT). The kinetic temperature of the molecular gas is 15-30 K in the eastern part and 30-50 K in the western part. The warmer gas is confined to a small region close to the compact H ii region S252A. The cooler gas is extended over the cloud even near the extended H ii region, the MHN. We made radio continuum observations at 8.4 GHz using the Yamaguchi 32 m radio telescope. The resultant map shows no significant extension from the Hα image. This means that the molecular cloud is less affected by the MHN, suggesting that the molecular cloud did not form by the expanding shock of the MHN. Although the spatial distribution of the Wide-field Infrared Survey Explorer and Two Micron All Sky Survey point sources suggests that triggered low-and intermediate-mass star formation took place locally around S252A, but the exciting star associated with it should be formed spontaneously in the molecular cloud.

The Astrophysical Journal, 2010

We report molecular line and dust continuum observations, made with the SEST telescope, towards four young high-mass star forming regions associated with highly luminous (L > 6 × 10 5 L ⊙ ) IRAS sources (15290-5546, 15502-5302, 15567-5236 and 16060-5146). Molecular emission was mapped in three lines of CS (J=2→1, 3→2 and 5→4), two lines of SiO (J=2→1 and 3→2), two rotational transitions of CH 3 OH (J k =3 k → 2 k and 2 k → 1 k ), and in the C 34 S(J=3→2) line.