* Astronomy

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Cepheus B

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NASA Chandra | Cepheus-B HD in 60 Seconds

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Space Telescopes Find Trigger-Happy Star Formation
A new study from two of NASA's Great Observatories provides fresh insight into how some stars are born, along with a beautiful new image of a stellar nursery in our Milky Way galaxy. The research shows that radiation from massive stars may trigger the formation of many more stars than previously thought.
While astronomers have long understood that stars and planets form from the collapse of a cloud of gas, the question of the main causes of this process has remained open.

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Position (2000): RA: 22h 56m 46.99s, Dec: 62° 40' 0.00"

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Title: Protoplanetary Disk Evolution Around the Triggered Star-Forming Region Cepheus B
Authors: Getman, Konstantin V.; Feigelson, Eric D.; Luhman, Kevin L.; Sicilia-Aguilar, Aurora; Wang, Junfeng; Garmire, Gordon P.

The Cepheus B (Cep B) molecular cloud and a portion of the nearby Cep OB3b OB association, one of the most active regions of star formation within 1 kpc, have been observed with the Infrared Array Camera detector on board the Spitzer Space Telescope. The goals are to study protoplanetary disk evolution and processes of sequential triggered star formation in the region. Out of ~400 pre-main-sequence (PMS) stars selected with an earlier Chandra X-ray Observatory observation, ~95% are identified with mid-infrared sources and most of these are classified as diskless or disk-bearing stars. The discovery of the additional >200 IR-excess low-mass members gives a combined Chandra+Spitzer PMS sample that is almost complete down to 0.5 M sun outside of the cloud, and somewhat above 1 M sun in the cloud. Analyses of the nearly disk-unbiased combined Chandra and Spitzer-selected stellar sample give several results. Our major finding is a spatio-temporal gradient of young stars from the hot molecular core toward the primary ionising O star HD 217086. This strongly supports the radiation-driven implosion (RDI) model of triggered star formation in the region. The empirical estimate for the shock velocity of ~1 km s^-1 is very similar to theoretical models of RDI in shocked molecular clouds. The initial mass function (IMF) of the lightly obscured triggered population exhibits a standard Galactic field IMF shape. The unusually high apparent value of gsim70% star formation efficiency inferred from the ratio of star mass to current molecular gas mass indicates that most of the Cep B molecular cloud has been already ablated or transformed to stars. Contrary to the current RDI simulations, our findings indicate that star formation triggering by H II region shocks is not restricted to a single episode but can continue for millions of years. Other results include: (1) agreement of the disk fractions, their mass dependency, and fractions of transition disks with other clusters; (2) confirmation of the youthfulness of the embedded Cep B cluster; (3) confirmation of the effect of suppression of time-integrated X-ray emission in disk-bearing versus diskless systems.

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Blobrana · L

Space Telescopes Find Trigger-Happy Star Formation
A new study from two of NASA's Great Observatories provides fresh insight into how some stars are born, along with a beautiful new image of a stellar nursery in our Milky Way galaxy. The research shows that radiation from massive stars may trigger the formation of many more stars than previously thought.
While astronomers have long understood that stars and planets form from the collapse of a cloud of gas, the question of the main causes of this process has remained open.
One option is that the cloud cools, gravity gets the upper hand, and the cloud falls in on itself. The other possibility is that a "trigger" from some external source -- like radiation from a massive star or a shock from a supernova -- initiates the collapse. Some previous studies have noted a combination of triggering mechanisms in effect.

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