arXiv subjects

A. F. Placinta-Mitrea

Publications and source records attributed to A. F. Placinta-Mitrea.

3 recordsLinked to original sources

arXiv2026

Discovery of thermal radio recombination line emission toward the high-mass protostar IRAS18162$-$2048

The physical conditions within the innermost few tens of au of high-mass protostars ($M_*>8~M_\odot$) remain largely unexplored. At these scales, ionised emission may trace photoionised gas, accretion disks, or the base of protostellar jets. We search for ionised emission in the form of radio recombination lines (RRLs) in high-mass star-forming regions. We use archival data from the Atacama Millimeter/submillimeter Array (ALMA) interferometer in band 6 ($\sim$1.3 mm) with a resolution of $θ_\mathrm{beam}\sim53~\mathrm{mas}\times42~\mathrm{mas}$ to examine the high-mass protostar IRAS18162$-$2048, driving source of the Herbig-Haro (HH) objects HH80-81. We detect, for the first time in this protostar, the thermal emission of the RRL H30$α$ ($\mathrm{rest~frequency}=231.90093$ GHz). The ionised emission is spatially unresolved in our observations, but we estimate an emitting region $\lesssim50$ au at the source distance of 1.4 kpc. The H30$α$ line profile is broad and spectrally resolved with a Local Standard of Rest velocity of $\sim-14~\mathrm{km~s^{-1}}$ (i.e., $\sim-26~\mathrm{km~s^{-1}}$ blue-shifted with respect to the systemic velocity of the cloud) and a full width at half maximum of $\sim82~\mathrm{km~s^{-1}}$. These observations suggest that the H30$α$ line is tracing outflowing blue-shifted material in the well-known radio jet from this object. This detection opens the possibility of detailed studies of the kinematics and physical properties of ionised jets.

astro-ph.GA↗

arXiv2026

Diverse stages of star formation in the IRAS 18162-2048 region. Emergence of UV Feedback

Methods: We obtained adaptive optics-assisted integral field spectroscopy in the near-infrared (IR) $K$ band ($1.93-2.47 \mathrm{μm}$) with VLT/SINFONI, complemented by VLA X and C bands (3$-$6 cm) and ALMA band 3 ($\sim$3.3 mm) observations. Results: The near-IR continuum reveals two infrared sources, IRS 2 and IRS 7, while the main protostellar core IRAS 18162-2048 remains undetected up to $2.47 \mathrm{μm}$. IRS 7 shows a peculiar Hydrogen Recombination Line Br$γ$ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence star. Extended H$_2$ emission exhibits a `sawtooth' pattern in the excitation diagram, characteristic of UV radiation in a PDR rather than shock excitation. The radiative transfer model Cloudy reproduces the H$_2$ ro-vibrational populations for $T_\mathrm{gas}=600$ K and $n_\mathrm{H}=7.9\times10^3 \mathrm{cm^{-3}}$. VLA X and C bands observations reveal a compact radio source previously reported as a stationary condensation (SC) and coincident with IRS 7. For the first time, we detect IRS 7/SC in mm wavelengths. The spectral index in the 3$-$6 cm and 3.3 mm regime is consistent with optically thin free-free emission. Conclusions: Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photoionise its environment, giving rise to an extended PDR and a compact \ion{H}{ii} region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field, suggests a multigenerational star-forming environment. Future \textit{James Webb Space Telescope} observations targeting the H$_2$ pure rotational lines ($3-28 \mathrm{μm}$) and other HRLs less affected by extinction will be essential to characterise the cooler molecular and ionised gas to fully disclose the formation history of the region.

astro-ph.GA↗

arXiv2025

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake. How do Planetary Systems Form?

The detection and characterization of protoplanets in protoplanetary disks around young stars is emerging as a transformative field that will redefine our understanding of how planetary systems form. While current facilities have revealed the diversity of mature exoplanets and the complex structures of disks, we still lack the crucial observational link between them: a statistically meaningful census of planets caught in the act of formation. This white paper argues that such a breakthrough requires access to the nearest and most informative star-forming regions, roughly half of which are poorly accessible or entirely unreachable from Cerro Armazones. Although the ELT alone will strongly impact our knowledge of planet formation, its location prevents Europe from fully exploiting the necessary parameter space. A 30-40 m telescope in the northern hemisphere is therefore essential for obtaining diffraction-limited imaging of protoplanets and disks across the entire sky, enabling robust demographics, exploiting synergies with ngVLA, Gaia, and other facilities covering the north, and ensuring that Europe remains at the forefront of the planet-formation revolution in the coming decades.

astro-ph.IM↗