The Rosette Eye: the key transition phase in the birth of a massive star

Massive protostars dramatically influence their surroundings via accretion-induced outflows and intense radiation fields. They evolve rapidly, the disk and infalling envelope being evaporated and dissipated in $\sim$ 10$^5$ years. Consequently, they are very rare and investigating this important phase of early stellar evolution is extremely difficult. Here we present the discovery of a key transient phase in the emergence of a massive young star, in which ultraviolet radiation from the new-born giant has just punctured through its natal core. The massive young stellar object AFGL 961 II is readily resolved in the near infrared. Its morphology closely resembles a cat's eye and is here dubbed as the Rosette Eye. Emerging ionized flows blow out an hourglass shaped nebula, which, along with the existence of strong near-infrared excess, suggests the existence of an accretion disk in the perpendicular direction. The lobes of the hourglass, however, are capped with arcs of static H$_{2}$ emission produced by fluorescence. This study has strong implications for our understanding of how massive stars embark on their formation.Comment: 3 figure

Asteroid Distributions in the Ecliptic

We present analysis of the asteroid surface density distribution of main belt asteroids (mean perihelion $\Delta \simeq 2.404$ AU) in five ecliptic latitude fields, -17 \gtsimeq \beta(\degr) \ltsimeq +15, derived from deep \textit{Large Binocular Telescope} (LBT) $V-$band (85% completeness limit $V = 21.3$ mag) and \textit{Spitzer Space Telescope} IRAC 8.0 \micron (80% completeness limit $\sim 103 \mu$Jy) fields enabling us to probe the 0.5--1.0 km diameter asteroid population. We discovered 58 new asteroids in the optical survey as well as 41 new bodies in the \textit{Spitzer} fields. The derived power law slopes of the number of asteroids per square degree are similar within each $\sim 5$\degr{} ecliptic latitude bin with a mean value of $-0.111 \pm 0.077$. For the 23 known asteroids detected in all four IRAC channels mean albedos range from $0.24 \pm 0.07$ to $0.10 \pm 0.05$. No low albedo asteroids ($p_{V}$ \ltsimeq 0.1) were detected in the \textit{Spitzer} FLS fields, whereas in the SWIRE fields they are frequent. The SWIRE data clearly samples asteroids in the middle and outer belts providing the first estimates of these km-sized asteroids' albedos. Our observed asteroid number densities at optical wavelengths are generally consistent with those derived from the Standard Asteroid Model within the ecliptic plane. However, we find an over density at \beta \gtsimeq 5\degr{} in our optical fields, while the infrared number densities are under dense by factors of 2 to 3 at all ecliptic latitudes.Comment: 35 pages including 5 figures, accepted to The Astronomical Journa

GM 2-4 - a signpost for low and intermediate mass star formation

We present a multi-wavelength study of the region towards the GM 2-4 nebula and the nearby source IRAS 05373+2340. Our near-infrared H2 1-0 S(1) line observations reveal various shock-excited features which are part of several bipolar outflows. We identify candidates for the driving sources of the outflows from a comparison of the multi-waveband archival data-sets and SED modelling. The SED spectral slope (\alpha(IRAC)) for all the protostars in the field was then compared with the visual extinction map. This comparison suggests that star formation is progressing from NE to SW across this region

Star-forming knots and density wave in NGC 2997

Context. Many grand design spiral galaxies show strings of bright knots along their arms on near-infrared K-band images. The alignment of such knots suggests a relation to the spiral pattern and possibly to a large-scale, star-forming front associated with a density wave. Aims. Bright knots in the southern arm of NGC 2997 were studied to determine their nature and evolutionary state. Methods. Low resolution near-infrared K- and J-band spectra of the knots were observed with ISAAC on the VLT. Results. Most of the knots show strong Hi Brγ emission with some also having He i and H2 emission. A few knots show indications of 12CO absorption. This suggests that the knots are very young stellar clusters with masses up to 5 × 104 Mʘ. Conclusions. The knots azimuthal distance from the K-band spiral correlates well with their Brγ strength, indicating that they are located inside the co-rotation of the density wave, which triggered them through a large-scale, star-forming front. These relative azimuthal distances suggest an age spread of more than 1.6Myr, which is incompatible with standard models for an instantaneous star burst. This indicates a more complex star-formation history, such as several bursts or continuous formation

The cores of ρ Ophiuchus

Abstract. We search for dense cores and the molecular outflows which accompany stellar birth in the rho Ophiuchi cloud L1688 through two unbiased wide-field surveys. A solution to the problem of how to avoid the dissolution of brown dwarf binaries is suggested: binaries forming in the widely scattered low-mass cores are not susceptible to disruption since the region is dynamically relaxed. We also find weak H 2 outflows which may be driven by proto-brown-dwarfs. The dense cores are detected through continuum emission from associated dust grains at 1.2 mm. Covering over 1 square degree, we detect many previously unknown sources, ranging from extended cores to those harbouring Class II young stars. We analyse the mass and spatial distributions. The core mass function resembles the stellar initial mass function, both within the tightly-packed clumps as well as within the less-crowded surroundings. The cores display a hierarchical spatial distribution with no preferred separation scale length. The orientations of the major axes of cores are consistent with an isotropic distribution whereas the orientations of core pairs possess a preferential direction on all separation scales, consistent with the filamentary cloud appearance. Our near-infrared survey for molecular hydrogen emission covers 35 × 35 . We detect several new H 2 flows but the total number of detected outflows is low and is consistent with the paucity of Class 0 and Class 1 sources in the molecular cloud. Most of the candidate driving sources are deeply embedded in dense cores. A very young outflow arises from the newly discovered Class 0 source MMS 126. Flow directions are generally NE-SW, perpendicular to the above preferred direction. The apparent extents of molecular flows are related to either the widths or the separation between cloud filaments

Isotope selective photodissociation of N 2 by the interstellar radiation field and cosmic rays

Context. Photodissociation of 14N2 and 14N 15N occurs in interstellar clouds, circumstellar envelopes, protoplanetary discs, and other environments due to ultraviolet radiation originating from stellar sources and the presence of cosmic rays. This sourc

Gm 2-4: a signpost for low- and intermediate-mass star formation★

We present a multi-wavelength study of the region towards the GM 2-4 nebula and the nearby source IRAS 05373+2340. Our near-infrared H2 10 S(1) line observations reveal various shock-excited features which are part of several bipolar outflows. We identify candidates for the driving sources of the outflows from a comparison of the multi-waveband archival data sets and spectral energy distribution (SED) modelling. The SED spectral slope () for all the protostars in the field was then compared with the visual extinction map. This comparison suggests that star formation progresses from north-east to south-west across this region