Understanding hydrogen recombination line observations with ALMA and EVLA

Peters, Thomas; Longmore, Steven N.; Dullemond, C. P.

doi:10.1111/j.1365-2966.2012.21676.x

Cited by 34 publications

(40 citation statements)

References 47 publications

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“…A possible drawback of (sub)mm RLs is that the free-free continuum may be contaminated by dust emission. Another problem is that they are out of LTE more easily than cm lines, so their interpretation may require careful modeling (e.g., Jiménez-Serra et al 2011;Peters et al 2012). As shown below, our simple LTE interpretation seems to be reasonable, but it is possible that a significant fraction of the 1.3-mm continuum comes from dust in the line of sight.…”

Section: Appendix A: Linewidth Of Recombination Linesmentioning

confidence: 88%

“…Millimeter (mm) RLs are in principle better suited to giving the central velocity of the system because they are more optically thin, much less pressure broadened, and intrinsically brighter than centimeter (cm) lines (e.g., Gordon & Sorochenko 2002;Peters et al 2012). However, longer wavelength lines are a valuable complement because they are sensitive to the gas density.…”

Section: Introductionmentioning

confidence: 99%

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ALMA and VLA observations of recombination lines and continuum toward the Becklin-Neugebauer object in Orion

Galván-Madrid

Goddi

Rodrı́guez

2012

A&A

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Compared to their centimeter-wavelength counterparts, millimeter recombination lines (RLs) are intrinsically brighter and are free of pressure broadening. We report observations of RLs (H30α at 231.9 GHz, H53α at 42.9 GHz) and the millimeter and centimeter continuum toward the Becklin-Neugebauer (BN) object in Orion, obtained from the Atacama Large Millimeter/submillimeter Array (ALMA) science verification archive and the Very Large Array (VLA). The RL emission appears to be arising from the slowly-moving, dense (N e = 8.4 × 10 6 cm −3 ) base of the ionized envelope around BN. This ionized gas has a relatively low electron temperature (T e < 4900 K) and small ( 10 km s −1 ) bulk motions. Comparing our continuum measurements with previous (non)detections, it is possible that BN has large flux variations in the millimeter. However, dedicated observations with a uniform setup are needed to confirm this. From the H30α line, the central line-of-sight LSR velocity of BN is 26.3 km s −1 .

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Section: Appendix A: Linewidth Of Recombination Linesmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

ALMA and VLA observations of recombination lines and continuum toward the Becklin-Neugebauer object in Orion

Galván-Madrid

Goddi

Rodrı́guez

2012

A&A

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“…Two are the most chemically rich in our study (G339.11, and G336.98, which, from its radio SED is expected to be one of our youngest Hii regions), while the other (G302.02) shows no molecular emission across the Hii region (neither in the H29α nor CS passbands), suggesting that the complex molecules have been destroyed by the ionising radiation. Peters et al (2012) implemented the modelling of RRL line profiles detectable at JVLA and ALMA wavelengths into RADMC-3D using non-LTE methods to understand line shapes. The test cases they used to demonstrate the code focussed on infalling and outflowing RRL emission, and under which conditions these signatures would be detectable.…”

Section: Rrl Velocity Gradientsmentioning

confidence: 99%

The evolution of young HII regions

Klaassen

Johnston

Urquhart

et al. 2018

A&A

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Context. High-mass stars form in much richer environments than those associated with isolated low-mass stars, and once they reach a certain mass, produce ionised (Hii) regions. The formation of these pockets of ionised gas are unique to the formation of high-mass stars (M > 8 M ), and present an excellent opportunity to study the final stages of accretion, which could include accretion through the Hii region itself. Aims. This study of the dynamics of the gas on both sides of these ionisation boundaries in very young Hii regions aims to quantify the relationship between the Hii regions and their immediate environments. Methods. We present high-resolution (∼ 0.5 ) ALMA observations of nine Hii regions selected from the Red MSX Source (RMS) survey with compact radio emission and bolometric luminosities greater than 10 4 L . We focus on the initial presentation of the data, including initial results from the radio recombination line H29α, some complementary molecules, and the 256 GHz continuum emission. Results. Of the six (out of nine) regions with H29α detections, two appear to have cometary morphologies with velocity gradients across them, and two appear more spherical with velocity gradients suggestive of infalling ionised gas. The remaining two were either observed at low resolution or had signals that were too weak to draw robust conclusions. We also present a description of the interactions between the ionised and molecular gas (as traced by CS (J=5-4)), often (but not always) finding the Hii region had cleared its immediate vicinity of molecules. Conclusions. Of our sample of nine, the observations of the two clusters expected to have the youngest Hii regions (from previous radio observations) are suggestive of having infalling motions in the H29α emission, which could be indicative of late stage accretion onto the stars despite the presence of an Hii region.

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“…As previously noted, they allowed for spherical outflow and found that line shapes can be asymmetric. Peters, Longmore, & Dullemond (2012) ii. The wind is optically thick to free-free opacity.…”

Section: Radio Recombination Line Modelingmentioning

confidence: 99%

Asymmetric Shapes of Radio Recombination Lines From Ionized Stellar Winds

Ignace

2019

RMxAA

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Recombination line profile shapes are derived for ionized spherical stellar winds at radio wavelengths. It is assumed that the wind is optically thick owing to free-free opacity. Emission lines of arbitrary optical depth are obtained assuming that the free-free photosphere forms in the outer, constant expansion portion of the wind. Previous works have derived analytic results for isothermal winds when the line and continuum source functions are equal. Here, semi-analytic results are derived for when the source functions are not equal to reveal that line shapes can be asymmetric about line center. A parameter study is presented and applications discussed.

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Understanding hydrogen recombination line observations with ALMA and EVLA

Cited by 34 publications

References 47 publications

ALMA and VLA observations of recombination lines and continuum toward the Becklin-Neugebauer object in Orion

ALMA and VLA observations of recombination lines and continuum toward the Becklin-Neugebauer object in Orion

The evolution of young HII regions

Asymmetric Shapes of Radio Recombination Lines From Ionized Stellar Winds

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