X-Ray Detection of the Ionizing Stars in Ultracompact H [CSC]ii[/CSC] Regions

Höfner, P.; Delgado, Hugo; Whitney, B. A.; Churchwell, E.; Linz, H.

doi:10.1086/345306

Cited by 38 publications

(41 citation statements)

References 20 publications

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“…The required X-ray flux of 10 erg s −1 cm −2 is far above the observed value from Hofner et al (2002) if the emitting X-ray source is near the center of the YSO. Thus, we cannot explain the observed ratios with irradiation of the central object(s) and the density expected from envelope models.…”

Section: Oh + To H 2 O + Ratiomentioning

confidence: 78%

“…4. The conclusion that FUV dominates over X-rays is similar for the high-mass object W3 IRS5, for which the reported X-ray luminosity is 5 × 10 30 erg s −1 (Hofner et al 2002). At Herschel's HPBR, this X-ray flux is geometrically attenuated to a level of 4 × 10 −6 erg s −1 cm −2 , which is not sufficient to produce the observed CH + /OH + ratio.…”

Section: Ch + To Oh + Ratiomentioning

confidence: 78%

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Water in star-forming regions withHerschel(WISH)

Benz

Bruderer

Dishoeck

et al. 2016

A&A

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Context. Hydrides are simple compounds containing one or a few hydrogen atoms bonded to a heavier atom. They are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides such as CH + and OH + (and also HCO + ), which affect the chemistry of molecules such as water, provide complementary information on irradiation by far-UV (FUV) or X-rays and gas temperature. Aims. We explore hydrides of the most abundant heavier elements in an observational survey covering young stellar objects (YSOs) with different mass and evolutionary state. The focus is on hydrides associated with the dense protostellar envelope and outflows, contrary to previous work that focused on hydrides in diffuse foreground clouds. Methods. Twelve YSOs were observed with HIFI on Herschel in six spectral settings providing fully velocity-resolved line profiles as part of the Water in star-forming regions with Herschel (WISH) program. The YSOs include objects of low (Class 0 and I), intermediate, and high mass, with luminosities ranging from 4 L to 2 × 10 5 L . Results. The targeted lines of CH + , OH + , H 2 O + , C + , and CH are detected mostly in blue-shifted absorption. H 3 O + and SH + are detected in emission and only toward some high-mass objects. The observed line parameters and correlations suggest two different origins related to gas entrained by the outflows and to the circumstellar envelope. The derived column densities correlate with bolometric luminosity and envelope mass for all molecules, best for CH, CH + , and HCO + . The column density ratios of CH + /OH + are estimated from chemical slab models, assuming that the H 2 density is given by the specific density model of each object at the beam radius. For the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400 times the interstellar radiation field (ISRF) at the location of the molecules. In two high-mass objects, the UV flux is 20-200 times the ISRF derived from absorption lines, and 300-600 ISRF using emission lines. Upper limits for the X-ray luminosity can be derived from H 3 O + observations for some low-mass objects. Conclusions. If the FUV flux required for low-mass objects originates at the central protostar, a substantial FUV luminosity, up to 1.5 L , is required. There is no molecular evidence for X-ray induced chemistry in the low-mass objects on the observed scales of a few 1000 AU. For high-mass regions, the FUV flux required to produce the observed molecular ratios is smaller than the unattenuated flux expected from the central object(s) at the Herschel beam radius. This is consistent with an FUV flux reduced by circumstellar extinction or by bloating of the protostar.

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Section: Oh + To H 2 O + Ratiomentioning

confidence: 78%

Section: Ch + To Oh + Ratiomentioning

confidence: 78%

Water in star-forming regions withHerschel(WISH)

Benz

Bruderer

Dishoeck

et al. 2016

A&A

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“…In Fig. 1a, we see that the emission decreases between SMM1/SMM2 and SMM3/SMM4/SMM5, dividing the cloud into two regions with the eastern part containing clusters of IR and cm-wave emission as well as X-ray emission (Hofner et al 2002), while the western part shows no IR and cmwave sources. This dichotomy implies that the eastern part of the source is more evolved and less embedded than the western part.…”

Section: Continuum Emissionmentioning

confidence: 97%

Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation

Wang

Bourke

Hogerheijde

et al. 2013

A&A

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Context. Two competing models describe the formation of massive stars in objects like the Orion Trapezium. In the turbulent core accretion model, the resulting stellar masses are directly related to the mass distribution of the cloud condensations. In the competitive accretion model, the gravitational potential of the protocluster captures gas from the surrounding cloud for which the individual cluster members compete. Aims. With high resolution submillimeter observations of the structure, kinematics, and chemistry of the proto-Trapezium cluster W3 IRS5, we aim to determine which mode of star formation dominates. Methods. We present 354 GHz Submillimeter Array observations at resolutions of 1 -3 (1800-5400 AU) of W3 IRS5. The dust continuum traces the compact source structure and masses of the individual cores, while molecular lines of CS, SO, SO 2 , HCN, H 2 CS, HNCO, and CH 3 OH (and isotopologues) reveal the gas kinematics, density, and temperature. Results. The observations show five emission peaks (SMM1-5). SMM1 and SMM2 contain massive embedded stars (∼20 M ); SMM3-5 are starless or contain low-mass stars (<8 M ). The inferred densities are high, ≥10 7 cm −3 , but the core masses are small, 0.2−0.6 M . The detected molecular emission reveals four different chemical zones. Abundant (X ∼ few 10 −7 to 10 −6 ) SO and SO 2 are associated with SMM1 and SMM2, indicating active sulfur chemistry. A low abundance (5 × 10 −8 ) of CH 3 OH concentrated on SMM3/4 suggest the presence of a hot core that is only just turning on, possibly by external feedback from SMM1/2. The gas kinematics are complex with contributions from a near pole-on outflow traced by CS, SO, and HCN; rotation in SO 2 , and a jet in vibrationally excited HCN. Conclusions. The proto-Trapezium cluster W3 IRS5 is an ideal test case to discriminate between models of massive star formation. Either the massive stars accrete locally from their local cores; in this case the small core masses imply that W3 IRS5 is at the very end stages (1000 yr) of infall and accretion, or the stars are accreting from the global collapse of a massive, cluster forming core. We find that the observed masses, densities and line widths observed toward W3 IRS 5 and the surrounding cluster forming core are consistent with the competitive accretion of gas at rates ofṀ ∼10 −4 M yr −1 by the massive young forming stars. Future mapping of the gas kinematics from large to small scales will determine whether large-scale gas inflow occurs and how the cluster members compete to accrete this material.

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“…In particular, the hard X-ray (>2 keV) imaging spectroscopy with ASCA has for the first time revealed several clumps in MFSRs, each showing a high temperature (3-10 keV) and a high luminosity (10 34 -10 34 ergs s À 1 ) (e.g., Yamauchi et al 1996;Hofner & Churchwell 1997;Nakano et al 2000;Sekimoto et al 2000). Thanks to its superb angular resolution, these X-ray clumps in MSFRs have been resolved into hundreds of stars with the Chandra X-Ray Observatory (e.g., Garmire et al 2000;Feigelson et al 2002Feigelson et al , 2003Hofner et al 2002;Kohno et al 2002;Nakajima et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Investigation of Diffuse Hard X‐Ray Emission from the Massive Star‐forming Region NGC 6334

Ezoe

Kokubun

Makishima

et al. 2006

ApJ

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Chandra ACIS-I data of the molecular cloud and H ii region complex NGC 6334 were analyzed. The hard X-ray clumps detected with ASCA (Sekimoto and coworkers) were resolved into 792 point sources. After removing the point sources, an extended X-ray emission component was detected over a 5 ; 9 pc 2 region, with the 0.5-8 keV absorption-corrected luminosity of 2 ; 10 33 ergs s À1 . The contribution from faint point sources to this extended emission was estimated as at most $20%, suggesting that most of the emission is diffuse in nature. The X-ray spectrum of the diffuse emission was observed to vary from place to place. In tenuous molecular cloud regions with hydrogen column density of (0:5 1) ; 10 22 cm À2 , the spectrum can be represented by a thermal plasma model with temperatures of several keV. The spectrum in dense cloud cores exhibits harder continuum, together with higher absorption of more than $3 ; 10 22 cm À2 . In some of such highly obscured regions, the spectra show extremely hard continua equivalent to a photon index of $1, and favor a nonthermal interpretation. These results are discussed in the context of thermal and nonthermal emission, both powered by fast stellar winds from embedded young early-type stars through shock transitions.

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X-Ray Detection of the Ionizing Stars in Ultracompact H [CSC]ii[/CSC] Regions

Cited by 38 publications

References 20 publications

Water in star-forming regions withHerschel(WISH)

Water in star-forming regions withHerschel(WISH)

Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation

Investigation of Diffuse Hard X‐Ray Emission from the Massive Star‐forming Region NGC 6334

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