Archive for Herbig-Haro objects

A new observational basis for star formation studies in Orion

Posted in astronomy with tags , , on March 8, 2016 by Tim Kendall

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A new paper entitled “VISION – Vienna Survey in Orion. I. VISTA Orion A Survey” is the first looking at the closest region of massive star formation – Orion. At the moment the complete paper by S. Meingast, J. Alves, D. Mardones, et al. (2016) is available here:

The Orion nebula cluster (ONC), the nearest region of massive star formation, is embedded in the much larger Orion A molecular cloud. The ONC has been studied much more extensively than other parts of Orion A, in spite of the opportunity that this region offers to understand the processes connected with the formation of both low- and high-mass stars. Using the ESO Visible and Infrared Survey Telescope for Astronomy (VISTA), the authors have surveyed the entire Orion A molecular cloud in the J, H, and K (short) near-infrared bands, covering a total of around 18.3 square degrees, and present the most detailed and sensitive near-infrared (NIR) observations of the entire molecular cloud to date. They find about 2500 embedded objects in Orion A and confirm the existence of a recently discovered foreground population above the Galactic field. The Orion A VISTA catalog contains 799 995 sources, which increases the source counts by about an order of magnitude compared to the 2MASS survey. It provides a basis for future studies of star formation processes toward Orion.

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Gemini views star formation in the Herbig-Haro object HH24

Posted in astronomy with tags , on October 2, 2015 by Tim Kendall

Gemini HH24Image and text credits: phys.org. The HH 24 jet complex emanates from a dense cloud core that hosts a small multiple protostellar system known as SSV63. The nebulous star to the south is the visible T Tauri star SSV59. Color image based on the following filters with composite image color assignments in parenthesis: g (blue), r (cyan), I (orange), hydrogen-alpha (red), sulphur II (blue) images obtained with GMOS on Gemini North in 0.5 arcsecond seeing, and NIRI. Field of view is 4.2×5.1 arcminutes, orientation: north up, east left. Credit: Gemini Observatory/AURA/B. Reipurth, C. Aspin, T. Rector

A new Gemini Observatory image reveals the remarkable “fireworks” that accompany the birth of stars. The image captures in unprecedented clarity the fascinating structures of a gas jet complex emanating from a stellar nursery at supersonic speeds. The striking new image hints at the dynamic (and messy) process of star birth. Researchers believe they have also found a collection of runaway (orphan) stars that result from all this activity. Gemini Observatory has released one of the most detailed images ever obtained of emerging gas jets streaming from a region of newborn stars. The region, known as the Herbig-Haro 24 (HH 24) Complex, contains no less than six jets streaming from a small cluster of embedded in a molecular cloud in the direction of the constellation of Orion.

“This is the highest concentration of jets known anywhere,” says Principal Investigator Bo Reipurth of the University of Hawaii’s Institute for Astronomy (IfA), who adds, “We also think the very dynamic environment causes some of the lowest mass stars in the area to be expelled, and our Gemini data are supporting that idea.” Reipurth along with co-researcher, Colin Aspin, also at the IfA, are using the Gemini North data from the Gemini Multi-Object Spectrograph (GMOS), as well as the Gemini Near-Infrared Imager, to study the region which was discovered in 1963 by George Herbig and Len Kuhi. Located in the Orion B cloud, at a distance of about 400 parsecs, or about 1,300 light-years from our Solar System, this region is rich in young stars and has been extensively studied in all types of light, from radio waves to X-rays.

“The Gemini data are the best ever obtained from the ground of this remarkable jet complex and are showing us striking new detail,” says Aspin. Reipurth and Aspin add that they are particularly interested in the fine structure and “excitation distribution” of these jets. “One jet is highly disturbed, suggesting that the source may be a close binary whose orbit perturbs the jet body,” says Reipurth. The researchers report that the jet complex emanates from what is called a Class I protostar, SSV63, which high-resolution infrared imaging reveals to have at least five components. More sources are found in this region, but only at longer, submillimeter wavelengths of light, suggesting that there are even younger, and more deeply embedded sources in the region. All of these embedded sources are located within the dense molecular cloud core.

A search for dim optical and infrared young stars has revealed several faint optical stars located well outside the star-forming core. In particular, a halo of five faint Hydrogen-alpha emission stars (which emit large amounts of red light) has been found with GMOS surrounding the HH 24 Complex well outside the dense cloud core. Gemini spectroscopy of the hydrogen alpha emission stars show that they are early or mid-M dwarfs (very low-mass stars), with at least one of which being a borderline brown dwarf. The presence of these five very low-mass stars well outside the star-forming cloud core is puzzling, because in their present location the gas is far too tenuous for the stars to have formed there. Instead they are likely orphaned protostars ejected shortly after birth from the nearby star-forming core. Such ejections occur when many stars are formed closely together within the same cloud core. The crowded stars start moving around each other in a chaotic dance, ultimately leading to the ejection of the smallest ones. A consequence of such ejections is that pairs of the remaining stars bind together gravitationally. The dense gas that surrounds the newly formed pairs brakes their motion, so they gradually spiral together to form tight binary systems with highly eccentric orbits. Each time the two components are closest in their orbits they disturb each other, leading to accretion of gas, and an outflow event that we see as supersonic jets. The many knots in the jets thus represent a series of such perturbations.

ALMA/NTT view of the Herbig-Haro object HH 46/47

Posted in astronomy with tags , on August 21, 2013 by Tim Kendall

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Image credit and caption: ESO/ALMA (ESO/NAOJ/NRAO)/H. Arce. Acknowledgements: Bo Reipurth. This unprecedented image of Herbig-Haro object HH 46/47 combines radio observations acquired with the Atacama Large Millimeter/submillimeter Array (ALMA) with much shorter wavelength visible light observations from ESO’s New Technology Telescope (NTT). The ALMA observations (orange and green, lower right) of the newborn star reveal a large energetic jet moving away from us, which in the visible is hidden by dust and gas. To the left (in pink and purple) the visible part of the jet is seen, streaming partly towards us.

ALMA Takes Close Look at Drama of Starbirth:

Young stars are violent objects that eject material at speeds as high as one million kilometres per hour. When this material crashes into the surrounding gas it glows, creating a Herbig-Haro object. A spectacular example is named Herbig-Haro 46/47 and is situated about 1400 light-years from Earth in the southern constellation of Vela (The Sails). This object was the target of a study using ALMA during the Early Science phase, whilst the telescope was still under construction and well before the array was completed.

The new images reveal fine detail in two jets, one coming towards Earth and one moving away. The receding jet was almost invisible in earlier pictures made in visible light, due to obscuration by the dust clouds surrounding the new-born star. ALMA has not only provided much sharper images than earlier facilities but also allowed astronomers to measure how fast the glowing material is moving through space.

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Isolated planetary-mass objects: “free-floating” planets do now appear to form in nature by the same process which forms stars. Previous research has shown that there may be as many as 200 billion free-floating planets in our galaxy, the Milky Way. Until now scientists have believed that such “rogue planets”, which don’t orbit around a star, must have been ejected from existing planetary systems. New observations of tiny dark clouds in space point out another possibility: that some free-floating planets formed on their own. A team of astronomers from Sweden and Finland used several telescopes to observe the Rosette Nebula, a huge cloud of gas and dust 4,600 light years from Earth in the constellation Monoceros (the Unicorn).

The paper of this research is now published; I have linked the preprint in an earlier post. The paper is “Mass and motion of globulettes in the Rosette Nebula”, G.F. Gahm et al., A&A, 555, A57 (2013).