Supernova-induced Star Formation Research Articles

Cloud Formation by Supernova Implosion

The deposition of energy and momentum by supernova explosions has been subject to numerous studies in the past few decades. However, while there has been some work that focused on the transition from the adiabatic to the radiative stage of a supernova remnant (SNR), the late radiative stage and merging with the interstellar medium (ISM) have received little attention. Here, we use three-dimensional, hydrodynamic simulations, focusing on the evolution of SNRs during the radiative phase, considering a wide range of physical explosion parameters ( nH,ISM∈0.1,100cm−3 and ESN∈1,14×1051erg ). We find that the radiative phase can be subdivided in four stages: A pressure-driven snowplow phase, during which the hot overpressurized bubble gas is evacuated and pushed into the cold shell; a momentum-conserving snowplow phase that is accompanied by a broadening of the shell; an implosion phase where cold material from the back of the shell is flooding the central vacuum; and a final cloud phase, during which the imploding gas is settling as a central, compact overdensity. The launching timescale for the implosion ranges from a few 100 kyr to a few Myr, while the cloud formation timescale ranges from a few to about 10 Myr. The highly chemically enriched clouds can become massive (M cl ∼ 103–104 M ⊙) and self-gravitating within a few Myr after their formation, providing an attractive, novel pathway for supernova-induced star and planet formation in the ISM.

A WISE CENSUS OF YOUNG STELLAR OBJECTS IN CANIS MAJOR

ABSTRACT With the Wide-field Infrared Survey Explorer (WISE), we searched for young stellar objects (YSOs) in a 100 deg2 region centered on the lightly studied Canis Major star-forming region. Applying stringent magnitude cuts to exclude the majority of extragalactic contaminants, we find 144 Class I candidates and 335 Class II candidates. The sensitivity to Class II candidates is limited by their faintness at the distance to Canis Major (assumed as 1000 pc). More than half the candidates (53%) are found in 16 groups of more than four members, including four groups with more than 25 members each. The ratio of Class II to Class I objects, N II/N I, varies from 0.4 to 8.3 in just the largest four groups. We compare our results to those obtainable with combined Two Micron All Sky Survey and post-cryogenic Spitzer Space Telescope data; the latter approach recovers missing Class II sources. Via a comparison to protostars characterized with the Herschel Space Observatory, we propose new WISE color criteria for flat-spectrum and Class 0 protostars, finding 80 and 7 of these, respectively. The distribution of YSOs in CMa OB1 is consistent with supernova-induced star formation, although the diverse N II/N I ratios are unexpected if this parameter traces age and the YSOs are due to the same supernova. Less massive clouds feature larger N II/N I ratios, suggesting that initial conditions play a role in determining this quantity.

Variations in the Abundance Pattern of Extremely Metal‐Poor Stars and Nucleosynthesis in Population III Supernovae

We calculate nucleosynthesis in Population (Pop) III supernovae (SNe) and compare the yields with various abundance patterns of extremely metal-poor (EMP) stars. We assume that the observed EMP stars are the second generation stars, which have the metal-abundance patterns of Pop III SNe. Previous theoretical yields of Pop III SNe cannot explain the trends in the abundance ratios among iron-peak elements (Mn, Co, Ni, Zn)/Fe as well as the large C/Fe ratio observed in certain EMP stars with [Fe/H] ~ 2) and low [Fe/H] (=~ -5 \~ -3.5) stars can be explained with the yields of faint SNe that eject little 56Ni as observed in SN1997D. In the supernova-induced star formation model, we can qualitatively explain why the EMP stars formed by the faint or energetic supernovae have lower [Fe/H] than the EMP stars formed by normal supernovae. We also examine how the abundance ratios among iron-peak elements depend on the electron mole fraction Ye, and conclude that a large explosion energy is still needed to realize the large Co/Fe and Zn/Fe ratios observed in typical EMP stars with [Fe/H] <~ -3.5.

Relics of Subluminous Supernovae in Metal-poor Stars

The unique elemental abundance pattern of the carbon-rich stars CS29498-043 and CS22949-037 is characterized by a large excess of magnesium and silicon in comparison with iron. This excess is investigated in the context of a supernova-induced star formation scenario, and it is concluded that these stars were born from the matter swept up by supernova remnants containing little iron and that such supernovae are similar to the least-luminous SNe ever observed, SNe 1997D and 1999br. Comparison of the observed abundance pattern in iron-group elements of subluminous supernovae with those of other supernovae leads to an intriguing implication for explosion, nucleosynthesis, and mixing in supernovae. The observed invariance of these ratios can not be accounted for by a spherically symmetric supernova model.

Star Formation History of ω Centauri Imprinted in Elemental Abundance Patterns

The star formation history of the globular cluster ω Centauri is investigated in the context of an inhomogeneous chemical evolution model in which supernovae induce star formation. The proposed model explains recent observations for ω Cen stars and divides star formation into three epochs. At the end of the first epoch, ~70% of the gas was expelled by supernovae. Asymptotic giant branch stars then supplied s-process elements to the remaining gas during the first interval of ~300 Myr. This explains the observed sudden increase in Ba/Fe ratios in ω Cen stars at [Fe/H] ~ -1.6. Supernovae at the end of the second epoch were unable to expel the gas. Eventually, Type Ia supernovae initiated supernova-induced star formation, and the remaining gas was stripped when the cluster passed through the newly formed disk of the Milky Way. The formation of ω Cen is also discussed in the framework of globular cluster formation triggered by cloud-cloud collisions. In this scenario, the relative velocity of clouds in the collision determines the later chemical evolution in the clusters. A head-on collision of protocluster clouds with a low relative velocity would have converted less than 1% of the gas into stars and promoted the subsequent chemical evolution by supernova-driven star formation. This is consistent with present observed form of ω Cen. In contrast, the other Galactic globular clusters are expected to have formed from more intense head-on collisions, and the resultant clouds would have been too thin for supernovae to accumulate enough gas to form the next generation of stars. This explains the absence of chemical evolution in these other globular clusters.

A Molecular Shell with Star Formation toward the Supernova Remnant G349.7+0.2

A field of about 38' × 38' around the supernova remnant (SNR) G349.7+0.2 has been surveyed in the CO J = 1–0 transition with the 12 m telescope of the NRAO, using the on-the-fly technique. The resolution of the observations is 54''. We have found that this remnant is interacting with a small CO cloud, which, in turn, is part of a much larger molecular complex, which we call the CO shell. The large CO shell has a diameter of about 100 pc, an H2 mass of 9.3 × 105 M⊙, and a density of 35 cm-3. We investigate the origin of this structure and suggest as a suitable hypothesis that an old supernova explosion occurred about 4 × 106 yr ago. Analyzing the interaction between G349.7+0.2 and the large CO shell, it is possible to determine that the shock front currently driven into the molecular gas is a nondissociative shock (C-type), in agreement with the presence of OH 1720 MHz masers. The positional and kinematic coincidence of one of the CO clouds that constitute the large CO shell, an IRAS pointlike source, and an ultracompact H II region indicates the presence of a recently formed star. We suggest that the formation of this star was triggered during the expansion of the large CO shell and suggest the possibility that the same expansion also created the progenitor star of G349.7+0.2. The large CO shell would then be one of the few observational examples of supernova-induced star formation.

Chemical Evolution of the Galactic Halo through Supernova-induced Star Formation and Its Implication for Population III Stars

A model for Galactic chemical evolution, driven by supernova-induced star formation, is formulated and used to examine the nature of the Galactic halo at early epochs. In this model, new stars are formed following each supernova event, thus their abundance pattern is determined by the combination of heavy elements ejected from the supernova itself and those elements which are already present in the interstellar gas swept up by the supernova remnant. The end result is a prediction of large scatter in the abundance ratios among low-metallicity stars, reflecting a different nucleosynthesis yield for each Type II supernova with a different progenitor mass. Formation of new stars is terminated when supernova remnants sweep up too little gas to form shells. We show from calculations based on the above scenario that (i) the observed [Fe/H] distribution for the Galactic halo field stars can be reproduced without effectively decreasing the heavy-element yields from Type II supernovae by some manipulation required by previous models (e.g., via mass loss from the early Galaxy, or later mixing with ``pristine'' hydrogen clouds), (ii) the large observed scatter in the abundance ratio [Eu/Fe] for the most metal-poor stars can also be reproduced, and (iii) the frequency distribution of stars in the [Eu/Fe]-[Fe/H] plane can be predicted. Our model suggests that the probability of identifying essentially metal-free stars (Population III) in the local halo is around one in 10^{3-4}, provided that star formation in the halo is confined to individual gas clouds with mass of 10^{6-7} Msun and that the initial mass function of metal-free stars is not significantly different from the Salpeter mass function.

Classical cepheids and the local chemical inhomogeneities in the galactic disc

Places of formation have been derived for a sample of 23 Cepheids with well-determined atmospheric abundances in an attempt to study the chemical inhomogeneities in the local interstellar medium. The abundance data available for the sample Cepheids is compiled and critically reviewed to adopt the most reliable esimates. We find that the most conspicuous irregularity in the metallicity is exhibited by stars that are born in the local arm or in the interarm region. We propose a scenario to explain these local variations in terms of supernova-induced star formation in interstellar gas enriched by massive stars formed in the density wave.

On the role of a supernova in the formation of the solar system

We consider four possible scenarios relating the proto-solar cloud to the “last-minute” supernova presumed responsible for the isotopic anomalies in Allende and other meteorites. The probability that a chance supernova occurred close enough to an already-collapsing proto-solar cloud to inject sufficient matter is extremely small, even if the Sun formed in a region of enhanced supernova activity such as Orion OB1. The ambient level of 26Al inside a molecular cloud in Orion is also apparently too low to account for the meteorite data, unless the supernova ejecta accumulates at the edges of the cloud and star formation occurs there preferentially. Two modes of supernova-induced star formation are discussed. In one, the supernova shock collapses a preexisting cloud; in the other, stars form within the snowplow shell of the supernova. Canis Major R1 and Monoceros R1 are possible present-day examples of such star formation regions.

Evidence for supernova-induced star formation in the monoceros OB2 association

The Monoceros ring, a circular optical nebulosity ∼3°.5 in diameter and centred at R.A.=6h37m, Dec.=6°30′ (lii=205°.5,bii=0°.2) is in good structural agreement with radio observations. A neutral hydrogen shell is also accurately projected on the ring. These observations are consistent with the Monoceros ring being a supernova remnant 90–100 pc in diameter expanding at about 45 km s−1 and having an age of the order of a million years. Bright Hii regions containing early-type stars (e.g., galactic cluster NGC 2244 in the Rosette nebula) and extremely young stars of the OB association Mon OB2 lie at the edges of the ring. The positional and temporal coincidence of the Mon OB2 association with a supernova remnant suggests that probably the star formation in this region is induced or speeded up by the passage of a supernova shock wave through the clumpy interstellar medium.

Supernova-induced star formation in Cepheus OB3

view Abstract Citations (41) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Supernova-induced star formation in Cepheus OB3. Assousa, G. E. ; Herbst, W. ; Turner, K. C. Abstract The neutral hydrogen distribution in the direction of Cep OB3 is reinvestigated, and the existence of an expanding shell confirmed. The expansion velocity, 35 km/s, and radius, 53 pc, imply that the feature is a supernova remnant (SNR) with an age of about 430,000 years. The younger subgroup of Cep OB3 has a comparable age, and it is suggested that this is another example of supernova-induced star formation. The kinematics of the association can also be explained by this hypothesis. The pulsar PSR 2223 + 65 may be a remnant of the SN event. Publication: The Astrophysical Journal Pub Date: November 1977 DOI: 10.1086/182566 Bibcode: 1977ApJ...218L..13A Keywords: Star Clusters; Star Formation; Supernova Remnants; B Stars; Hydrogen Clouds; O Stars; Supernovae; Astrophysics full text sources ADS | data products SIMBAD (3)

Observational evidence for supernova-induced star formation - Canis Major R1

view Abstract Citations (177) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observational evidence for supernova-induced star formation: Canis Major R1. Herbst, W. ; Assousa, G. E. Abstract Observational evidence is presented which indicates that star formation in the young association CMa R1 was initiated by a supernova explosion (probably of Type II) that occurred about half a million years ago. Palomar Sky Survey prints, neutral-hydrogen maps, and radial-velocity data are examined which show that the CMa R1 association is located on the outer edge of a ring of optical and radio emission, that an expanding neutral-hydrogen shell is coincident with the optical feature, and that HD 54662 is a runaway star in the CMa OB1 association and may be associated with the event that produced the observed supernova remnant. The optical and radio features are interpreted as a supernova remnant with an age of about 500,000 years and an initial outburst energy of the order of 5 by 10 to the 50th power ergs, which is expanding into an initially nonuniform medium characterized by an initial atomic-hydrogen density of approximately 1 per cu cm in the direction toward CMa R1 and less than half that value in the direction toward the sun. Publication: The Astrophysical Journal Pub Date: October 1977 DOI: 10.1086/155596 Bibcode: 1977ApJ...217..473H Keywords: Early Stars; Nebulae; Star Formation; Supernova Remnants; Astronomical Maps; Astronomical Photography; Hydrogen Clouds; Protostars; Ring Structures; Sky Surveys (Astronomy); Stellar Models; Astrophysics full text sources ADS | data products SIMBAD (18)