arXiv subjects

M. A. Trinidad

Publications and source records attributed to M. A. Trinidad.

12 recordsLinked to original sources

arXiv2026

Physical characterization and modeling of candidate Hyper-Compact HII Regions

Hypercompact HII regions (HC) are regions of ionized gas associated with the early stages of high-mass star formation. With the aim of better understanding their characteristics, we studied five candidate HC HII regions. Here, we present observations with the Jansky Very Large Array (VLA) at 2 and 6 cm, with angular resolutions in the range of $\sim$1 -- 3\arcsec and report the images of the detected sources and the measured parameters. In addition, we explore several possible scenarios, considering the regions as both uniform and non-uniform spheres, and as winds, both spherical and collimated. In most cases, the sources were unresolved, but by applying the models, we estimate that their sizes vary in a range of 0.3 to 3.7 mpc while their electron densities are in the range of $1.3 \times 10^{5}$ to $2.4 \times 10^{6}$ cm$^{-3}$, indicating that most sources are consistent with small, weak UC HII regions, although a few remain viable candidates for HC HII regions, with G40.28$-$0.22 as the strongest case. We do not rule out the possibility that some sources are jets or stellar winds.

astro-ph.GA↗

arXiv2023

Nobeyama Cygnus-X Survey: Physical Properties of C$^{18}$O clumps in DR-6(W), DR-9 and DR-13S regions

Cygnus-X is considered a region of interest for high-energy astrophysics, since the Cygnus OB2 association has been confirmed as a PeVatron in the Cygnus cocoon. In this research note, we present new high-resolution (16'') $^{12,13}$CO(J=1$\rightarrow$0) and C$^{18}$O (J=1$\rightarrow$0) observations obtained with the Nobeyama 45-m radiotelescope, to complement the Nobeyama Cygnus-X Survey. We discovered 19 new C$^{18}$O clumps associated with the star-forming regions DR-6W, DR-9, and DR13S. We present the physical parameters of these clumps, which are consistent with the neighboring covered regions. We confirm the clumpy nature of these regions and of a filament located between DR6 and DR6W. These results strongly suggest that star formation occurs in these regions with clumps of sizes $\sim$10$^{-1}$ pc, masses $\sim$10$^2$ M$_\odot$, and H$_2$ densities of $\sim$10$^4$ cm$^{-3}$.

astro-ph.GA↗

arXiv2023

Search and study of ultracompact HII regions

We present results from a sample of 106 high-luminosity IRAS sources observed with the Very Large Array in the B and C configurations. 96 sources were observed in the X-band and 52 in the K-band, with 42 of them observed at both wavelengths. We also used previously published observations in the C-band for 14 of them. The detection rate of sources with 3.6~cm continuum emission was $\sim25\%$, while only 10\% have emission at 1.3~cm. In order to investigate the nature of these sources, their physical parameters were calculated mainly using the 3.6~cm continuum emission, and for sources detected at two wavelengths, we used the best fit of three HII region models with different geometries. As a final result, we present a catalog of the detected sources, which includes their basic physical parameters for further analysis. The catalog contains 17 ultracompact HII regions and 3 compact HII regions.

astro-ph.GA↗

arXiv2017

Proper motions of L1551 IRS 5 binary system using 7 mm VLA observations

We analyzed high angular resolution observations of the Very Large Array archive at a wavelength of 7 mm of the L1551 IRS 5 binary system. Six sets of observations,five with the A configuration and one with the B configuration, were used, covering a time span of about 15 years. With these multi-epoch data, we estimated the absolute and relative proper motions of the binary system, which are about 25.1 mas/yr (~ 16.7 km/s considering a distance of 140 pc) and 4.2 mas/yr, respectively. Finally, based on the relative proper motion, we estimated a total mass of the L1551 IRS 5 binary system of 1.7 Msun and an orbital period of 246 years.

astro-ph.SR↗

arXiv2016

SMA observations towards the compact, short-lived bipolar water maser outflow in the LkHα 234 region

We present Submillimeter Array (SMA) 1.35 mm subarcsecond angular resolution observations toward the LkHα 234 intermediate-mass star-forming region. The dust emission arises from a filamentary structure of $\sim$5 arcsec ($\sim$4500 au) enclosing VLA 1-3 and MM 1, perpendicular to the different outflows detected in the region. The most evolved objects are located at the southeastern edge of the dust filamentary structure and the youngest ones at the northeastern edge. The circumstellar structures around VLA 1, VLA 3, and MM 1 have radii between $\sim$200 and $\sim$375 au and masses in the $\sim$0.08-0.3 M$_{\odot}$ range. The 1.35 mm emission of VLA 2 arises from an unresolved (r$< 135$ au) circumstellar disk with a mass of $\sim$0.02 M$_{\odot}$. This source is powering a compact ($\sim$4000 au), low radial velocity ($\sim$7 km s$^{-1}$) SiO bipolar outflow, close to the plane of the sky. We conclude that this outflow is the "large-scale" counterpart of the short-lived, episodic, bipolar outflow observed through H$_2$O masers at much smaller scales ($\sim $180 au), and that has been created by the accumulation of the ejection of several episodic collimated events of material. The circumstellar gas around VLA 2 and VLA 3 is hot ($\sim$130 K) and exhibits velocity gradients that could trace rotation. There is a bridge of warm and dense molecular gas connecting VLA 2 and VLA 3. We discuss the possibility that this bridge could trace a stream of gas between VLA 3 and VLA 2, increasing the accretion rate onto VLA 2 to explain why this source has an important outflow activity.

astro-ph.GA↗

arXiv2016

Evolution of electron beam pulses of short duration in the solar corona

Narrowband radio bursts with durations of the order of milliseconds, called spikes, are known to be associated with solar flares. In order to understand the particle beams responsible for the radio spike phenomena, evolution of electron beam pulses injected from a solar flare region into the corona is studied. Numerical integration of the Fokker-Planck (FP) equation is used to follow the evolution of the electron beam pulse. The simulations show that the short duration pulses lose most of their energy within a second of propagation into the corona. Electron beam with a small low energy cut off is thermalised faster than that with a high low energy cut off.

astro-ph.SR↗

arXiv2015

Time series of high resolution spectra of SN 2014J observed with the TIGRE telescope

We present a time series of high resolution spectra of the Type Ia supernova 2014J, which exploded in the nearby galaxy M82. The spectra were obtained with the HEROS echelle spectrograph installed at the 1.2 m TIGRE telescope. We present a series of 33 spectra with a resolution of R = 20, 000, which covers the important bright phases in the evolution of SN 2014J during the period from January 24 to April 1 of 2014. The spectral evolution of SN 2014J is derived empirically. The expansion velocities of the Si II P-Cygni features were measured and show the expected decreasing behaviour, beginning with a high velocity of 14,000 km/s on January 24. The Ca II infrared triplet feature shows a high velocity component with expansion velocities of > 20, 000 km/s during the early evolution apart from the normal component showing similar velocities as Si II. Further broad P-Cygni profiles are exhibited by the principal lines of Ca II, Mg II and Fe II. The TIGRE SN 2014J spectra also resolve several very sharp Na I D doublet absorption components. Our analysis suggests interesting substructures in the interstellar medium of the host galaxy M82, as well as in our Milky Way, confirming other work on this SN. We were able to identify the interstellar absorption of M82 in the lines of Ca II H & K at 3933 and 3968 A as well as K I at 7664 and 7698 A. Furthermore, we confirm several Diffuse Interstellar Bands, at wavelengths of 6196, 6283, 6376, 6379 and 6613 A and give their measured equivalent widths.

astro-ph.HE↗

arXiv2014

A very young, compact bipolar H$_2$O maser outflow in the intermediate-mass star-forming LkH$α$ 234 region

We report multi-epoch VLBI H$_2$O maser observations towards the compact cluster of YSOs close to the Herbig Be star LkH$α$ 234. This cluster includes LkH$α$ 234 and at least nine more YSOs that are formed within projected distances of $\sim$10 arcsec ($\sim$9,000 au). We detect H$_2$O maser emission towards four of these YSOs. In particular, our VLBI observations (including proper motion measurements) reveal a remarkable very compact ($\sim$0.2 arcsec = $\sim$180 au), bipolar H$_2$O maser outflow emerging from the embedded YSO VLA 2. We estimate a kinematic age of $\sim$40 yr for this bipolar outflow, with expanding velocities of $\sim$20 km s$^{-1}$ and momentum rate $\dot M_w V_w$ $\simeq$ $10^{-4}-10^{-3}$ M$_{\odot}$ yr$^{-1}$ km s$^{-1}$$\times (Ω$/$4π)$, powered by a YSO of a few solar masses. We propose that the outflow is produced by recurrent episodic jet ejections associated with the formation of this YSO. Short-lived episodic ejection events have previously been found towards high-mass YSOs. We show now that this behaviour is also present in intermediate-mass YSOs. These short-lived episodic ejections are probably related to episodic increases in the accretion rate, as observed in low-mass YSOs. We predict the presence of an accretion disk associated with VLA 2. If detected, this would represent one of the few known examples of intermediate-mass stars with a disk-YSO-jet system at scales of a few hundred au.

astro-ph.SR↗

arXiv2013

Multi-epoch VLBA H$_2$O maser observations toward the massive YSOs AFGL 2591 VLA 2 and VLA 3

We present multi-epoch Very Long Baseline Array (VLBA) H$_2$O maser observations toward the massive young stellar objects (YSOs) VLA 2 and VLA 3 in the star-forming region AFGL 2591. Through these observations, we have extended the study of the evolution of the masers towards these objects up to a time span of $\sim$ 10 yrs, measuring their radial velocities and proper motions. The H$_2$O masers in VLA 3, the most massive YSO in AFGL 2591 ($\sim$ 30--40~M$_{\odot}$), are grouped within projected distances of $\lesssim$ 40 mas ($\lesssim$ 130 AU) from VLA 3. In contrast to other H$_2$O masers in AFGL 2591, the masers associated with VLA 3 are significantly blueshifted (up to $\sim$ 30 km s$^{-1}$) with respect to the velocity of the ambient molecular cloud. We find that the H$_2$O maser cluster as a whole, has moved westwards of VLA~3 between the 2001 and 2009 observations, with a proper motion of $\sim$ 1.2 mas yr$^{-1}$ ($\sim$ 20 km s$^{-1}$). We conclude that these masers are tracing blueshifted outflowing material, shock excited at the inner parts of a cavity seen previously in ammonia molecular lines and infrared images, and proposed to be evacuated by the outflow associated with the massive VLA 3 source. The masers in the region of VLA 2 are located at projected distances of $\sim$ 0.7$''$ ($\sim$ 2300 AU) north from this source, with their kinematics suggesting that they are excited by a YSO other than VLA 2. This driving source has not yet been identified.

astro-ph.GA↗

arXiv2012

Formation and evolution of the water maser outflow event in AFGL 2591 VLA 3-N

In this paper we analyze multi-epoch Very Long Baseline Interferometry (VLBI) water maser observations carried out with the Very Long Baseline Array (VLBA) toward the high-mass star-forming region AFGL 2591. We detected maser emission associated with the radio continuum sources VLA 2 and VLA 3. In addition, a water maser cluster, VLA 3-N, was detected ~ 0.5" north of VLA 3. We concentrate the discussion of this paper on the spatio-kinematical distribution of the water masers towards VLA 3-N. The water maser emission toward the region VLA 3-N shows two bow shock-like structures, Northern and Southern, separated from each other by ~ 100 mas (~ 330 AU). The spatial distribution and kinematics of the water masers in this cluster have persisted over a time span of seven years. The Northern bow shock has a somewhat irregular morphology, while the Southern one has a remarkably smooth morphology. We measured the proper motions of 33 water maser features, which have an average proper motion velocity of ~ 1.3 mas/yr (~ 20 km/s). The morphology and the proper motions of this cluster of water masers show systematic expanding motions that could imply one or two different centers of star formation activity. We made a detailed model for the Southern structure, proposing two different kinematic models to explain the 3-dimensional spatio-kinematical distribution of the water masers: (1) a static central source driving the two bow-shock structures; (2) two independent driving sources, one of them exciting the Northern bow-shock structure, and the other one, a young runaway star moving in the local molecular medium exciting and molding the remarkably smoother Southern bow-shock structure. Future observations will be necessary to discriminate between the two scenarios, in particular by identifying the still unseen driving source(s).

astro-ph.SR↗

arXiv2008

Spitzer--IRAC Imagery and Photometry of Ultracompact HII Regions With Extended Emission

We present the results of a morphological study performed to a sample of Ultracompact (UC) HII regions with Extended Emission (EE) using Spitzer--IRAC imagery and 3.6 cm VLA conf. D radio-continuum (RC) maps. Some examples of the comparison between maps and images are presented. Usually there is an IR point source counterpart to the peak(s) of RC emission, at the position of the UC source. We find that the predominant EE morphology is the cometary, and in most cases is coincident with IR emission at 8.0 $μ$m. Preliminary results of Spitzer--IRAC photometry of a sub-sample of 13 UC HII regions with EE based on GLIMPSE legacy data are also presented. Besides, individual IRAC photometry was performed to 19 UC sources within these 13 regions. We show that UC sources lie on specific locus, both in IRAC color-color and AM-product diagnostic diagrams. Counts of young stellar sources are presented for each region, and we conclude that a proportion of ~ 2%, ~10%, and ~88% of sources in the UC HII regions with EE are, in average, Class I, II, and III, respectively.

astro-ph↗

arXiv2007

Multiple Sources toward the High-mass Young Star S140 IRS1

S140 IRS1 is a remarkable source where the radio source at the center of the main bipolar molecular outflow in the region is elongated perpendicular to the axis of the outflow, an orientation opposite to that expected if the radio source is a thermal jet exciting the outflow. We present results of 1.3 cm continuum and H2O maser emission observations made with the VLA in its A configuration toward this region. In addition, we also present results of continuum observations at 7 mm and re-analyse observations at 2, 3.5 and 6 cm (previously published). IRS 1A is detected at all wavelengths, showing an elongated structure. Three water maser spots are detected along the major axis of the radio source IRS 1A. We have also detected a new continuum source at 3.5 cm (IRS 1C) located ~0.6'' northeast of IRS 1A. The presence of these two YSOs (IRS 1A and 1C) could explain the existence of the two bipolar molecular outflows observed in the region. In addition, we have also detected three continuum clumps (IRS 1B, 1D and 1E) located along the major axis of IRS 1A. We discuss two possible models to explain the nature of IRS 1A: a thermal jet and an equatorial wind.

astro-ph↗