Aida Ahmadi

Aida Ahmadi
Leiden University | LEI · Leiden Observatory

PhD

About

66
Publications
2,527
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
652
Citations
Citations since 2016
64 Research Items
643 Citations
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200

Publications

Publications (66)
Article
Full-text available
The IRAM CORE large program combines data from NOEMA and the IRAM 30m telescope to study a diverse set of physical and chemical processes during the formation of high-mass stars. Here, we present a selected compilation of exciting results obtained during the survey.
Preprint
No statistical study of COMs toward a large sample of high-mass protostars with ALMA has been carried out so far. We aim to study six N-bearing species: CH$_3$CN, HNCO, NH$_2$CHO, C$_2$H$_5$CN, C$_2$H$_3$CN and CH$_3$NH$_2$ in a large sample of high-mass protostars. From the ALMAGAL survey, 37 of the most line-rich hot molecular cores are selected....
Article
Full-text available
Context . The deuteration of molecules forming in the ices such as methanol (CH 3 OH) is sensitive to the physical conditions during their formation in dense cold clouds and can be probed through observations of deuterated methanol in hot cores. Aims . The aim is to determine the D/H ratio of methanol for a large sample of 99 high-mass protostars a...
Preprint
The deuteration of molecules forming in the ices such as methanol (CH$_3$OH) is sensitive to the physical conditions during their formation in dense cold clouds and can be probed through observations of deuterated methanol in hot cores. Observations with ALMA containing transitions of CH$_3$OH, CH$_2$DOH, CHD$_2$OH, $^{13}$CH$_3$OH, and CH$_3^{18}$...
Article
Context. Complex organic molecules (COMs) are often observed toward embedded Class 0 and I protostars. However, not all Class 0 and I protostars exhibit COM emission. Aims. The aim is to study variations in methanol (CH 3 OH) emission and use this as an observational tracer of hot cores to test if the absence of CH 3 OH emission can be linked to so...
Preprint
Complex organic molecules (COMs) are often observed toward embedded Class 0 and I protostars. However, not all Class 0 and I protostars exhibit COMs emission. In this work, variations in methanol (CH$_3$OH) emission are studied to test if absence of CH$_3$OH emission can be linked to source properties. Combining both new and archival observations w...
Article
Context. To better understand the formation of high-mass stars, it is fundamental to investigate how matter accretes onto young massive stars, how it is ejected, and how all this differs from the low-mass case. The massive protocluster G31.41+0.31 is the ideal target to study all these processes because observations at millimeter and centimeter wav...
Preprint
Full-text available
Context. To better understand the formation of high-mass stars, it is fundamental to investigate how matter accretes onto young massive stars, how it is ejected, and how all this differs from the low-mass case. The massive protocluster G31.41+0.31 is the ideal target to study all these processes because observations at millimeter and centimeter wav...
Article
Context. Increasing evidence suggests that, similar to their low-mass counterparts, high-mass stars form through a disk-mediated accretion process. At the same time, formation of high-mass stars still necessitates high accretion rates, and hence, high gas densities, which in turn can cause disks to become unstable against gravitational fragmentatio...
Preprint
Full-text available
Increasing evidence suggests that, similar to their low-mass counterparts, high-mass stars form through a disk-mediated accretion process. At the same time, formation of high-mass stars still necessitates high accretion rates, and hence, high gas densities, which in turn can cause disks to become unstable against gravitational fragmentation. We stu...
Article
Full-text available
Context. Increasing evidence suggests that, similar to their low-mass counterparts, high-mass stars form through a disk-mediated accretion process. At the same time, formation of high-mass stars still necessitates high accretion rates, and hence, high gas densities, which in turn can cause disks to become unstable against gravitational fragmentatio...
Article
Theoretical and numerical works indicate that a strong magnetic field should suppress fragmentation in dense cores. However, this has never been tested observationally in a relatively large sample of fragmenting massive dense cores. Here, we use the polarization data obtained in the Submillimeter Array Legacy Survey of Zhang et al. to build a sampl...
Article
Context. The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research. Aims. We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation. Methods. Employing the NOrthern Extended Millim...
Preprint
Context: The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research. Aims: We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation. Methods: Employing the NOrthern Extended Millim...
Article
Full-text available
Aims: Current star formation research centers the characterization of the physical and chemical properties of massive stars, which are in the process of formation, at the spatial resolution of individual high-mass cores. Methods: We use sub-arcsecond resolution (~0.′′4) observations with the NOrthern Extended Millimeter Array at 1.37 mm to study th...
Article
Context. ALMA observations at 1.4 mm and ~0.′′2 (~750 au) angular resolution of the Main core in the high-mass star-forming region G31.41+0.31 have revealed a puzzling scenario. On the one hand, the continuum emission looks very homogeneous and the core appears to undergo solid-body rotation, suggesting a monolithic core stabilized by the magnetic...
Preprint
Context. ALMA observations at 1.4 mm and 0.2'' (750au) angular resolution of the Main core in the high-mass star forming region G31.41+0.31 have revealed a puzzling scenario: on the one hand, the continuum emission looks very homogeneous and the core appears to undergo solid-body rotation, suggesting a monolithic core stabilized by the magnetic fie...
Article
Context. Star formation (SF) is a multi-scale process in which the mode of fragmentation of the collapsing clump on scales of 0.1–1 pc determines the mass reservoir and affects the accretion process of the individual protostars on scales of 10–100 au. Aims. We want to investigate the nearby (located at 1.63 ± 0.05 kpc) high-mass star-forming regio...
Article
Aims. Current star formation research centers the characterization of the physical and chemical properties of massive stars, which are in the process of formation, at the spatial resolution of individual high-mass cores. Methods. We use sub-arcsecond resolution (~0.′′4) observations with the NOrthern Extended Millimeter Array at 1.37 mm to study th...
Preprint
Full-text available
We use sub-arcsecond resolution ($\sim$0.4$''$) observations with NOEMA at 1.37 mm to study the dust emission and molecular gas of 18 high-mass star-forming regions. We combine the derived physical and chemical properties of individual cores in these regions to estimate their ages. The temperature structure of these regions are determined by fittin...
Preprint
Full-text available
In the massive star-forming region IRAS 21078+5211, a highly fragmented cluster (0.1~pc in size) of molecular cores is observed, located at the density peak of an elongated (1~pc in size) molecular cloud. A small (1~km/s per 0.1~pc) LSR velocity (Vlsr) gradient is detected across the axis of the molecular cloud. Assuming we are observing a mass flo...
Article
Context. Star formation (SF) is a multi-scale process in which the mode of fragmentation of the collapsing clump on scales of 0.1–1 pc determines the mass reservoir and affects the accretion process of the individual protostars on scales of 10–100 au. Aims. We want to investigate the nearby (located at 1.63 ± 0.05 kpc) high-mass star-forming region...
Article
Aims. Methyl isocyanate (CH 3 NCO) and glycolonitrile (HOCH 2 CN) are isomers and prebiotic molecules that are involved in the formation of peptide structures and the nucleobase adenine, respectively. These two species are investigated to study the interstellar chemistry of cyanides (CN) and isocyanates (NCO) and to gain insight into the reservoir...
Preprint
Full-text available
Methyl isocyanate (CH$_{3}$NCO) and glycolonitrile (HOCH$_{2}$CN) are isomers and prebiotic molecules that are involved in the formation of peptide structures and the nucleobase adenine, respectively. ALMA observations of the intermediate-mass Class 0 protostar Serpens SMM1-a and ALMA-PILS data of the low-mass Class 0 protostar IRAS~16293B are used...
Article
The formation of hot stars out of the cold interstellar medium lies at the heart of astrophysical research. Understanding the importance of magnetic fields during star formation remains a major challenge. With the advent of the Atacama Large Millimeter Array, the potential to study magnetic fields by polarization observations has tremendously progr...
Preprint
Full-text available
Theoretical and numerical works indicate that a strong magnetic field should suppress fragmentation in dense cores. However, this has never been tested observationally in a relatively large sample of fragmenting massive dense cores. Here we use the polarization data obtained in the Submillimeter Array Legacy Survey of Zhang et al. (2014) to build a...
Preprint
The formation of hot stars out of the cold interstellar medium lies at the heart of astrophysical research. Understanding the importance of magnetic fields during star formation remains a major challenge. With the advent of the Atacama Large Millimeter Array, the potential to study magnetic fields by polarization observations has tremendously progr...
Article
We have studied the dust density, temperature, and velocity distributions of the archetypal massive young stellar object (MYSO) AFGL 2591. Given its high luminosity ($L=2\times 10^5\, \mbox{L$_{\odot}$}$) and distance (d = 3.3 kpc), AFGL 2591 has one of the highest $\sqrt{L}/d$ ratio, giving better resolved dust emission than any other MYSO. As suc...
Preprint
Full-text available
We have studied the dust density, temperature and velocity distributions of the archetypal massive young stellar object (MYSO) AFGL 2591. Given its high luminosity ($L=2 \times 10^5$ L$_\odot$) and distance ($d=3.3$ kpc), AFGL 2591 has one of the highest $\sqrt{L}/d$ ratio, giving better resolved dust emission than any other MYSO. As such, this pap...
Article
Full-text available
Context. High-mass star formation typically takes place in a crowded environment, with a higher likelihood of young forming stars affecting and being affected by their surroundings and neighbours, as well as links between different physical scales affecting the outcome. However, observational studies are often focused on either clump or disc scales...
Article
Full-text available
Context. High-mass star formation typically takes place in a crowded environment, with a higher likelihood of young forming stars affecting and being affected by their surroundings and neighbours, as well as links between different physical scales affecting the outcome. However, observational studies are often focused on either clump or disc scales...
Article
We present high-resolution (30 mas or 130 au at 4.2 kpc) Atacama Large Millimeter/submillimeter Array observations at 1.2 mm of the disc around the forming O-type star AFGL 4176 mm1. The disc (AFGL 4176 mm1-main) has a radius of ∼1000 au and contains significant structure, most notably a spiral arm on its redshifted side. We fitted the observed spi...
Thesis
Full-text available
This thesis is dedicated to the search and characterization of disks in high-mass star formation. The work presented is part of the CORE survey, a large observational program making use of interferometric observations from the NOrthern Extended Millimetre Array (NOEMA)for a sample of 20 high-mass protostellar objects in the 1.3 millimetre wavelengt...
Preprint
We present high-resolution (30 mas or 130 au at 4.2 kpc) Atacama Large Millimeter/submillimeter Array observations at 1.2 mm of the disk around the forming O-type star AFGL 4176 mm1. The disk (AFGL 4176 mm1-main) has a radius of $\sim$1000 au and contains significant structure, including a spiral arm on its redshifted side. By fitting the spiral wi...
Article
Full-text available
Aims. In order to understand the observed molecular diversity in high-mass star-forming regions, we have to determine the underlying physical and chemical structure of those regions at high angular resolution and over a range of evolutionary stages. Methods. We present a detailed observational and modeling study of the hot core VLA 3 in the high-ma...
Article
Full-text available
Context. In the disc-mediated accretion scenario for the formation of the most massive stars, high densities and high accretion rates could induce gravitational instabilities in the disc, forcing it to fragment and produce companion objects. Aims. We investigate the effects of inclination and spatial resolution on the observable kinematics and stab...
Article
Full-text available
Aims. In order to understand the observed molecular diversity in high-mass star-forming regions, we have to determine the underlying physical and chemical structure of those regions at high angular resolution and over a range of evolutionary stages. Methods. We present a detailed observational and modeling study of the hot core VLA 3 in the high-ma...
Preprint
We present a detailed observational and modeling study of the hot core VLA 3 in the high-mass star-forming region AFGL 2591, which is a target region of the NOrthern Extended Millimeter Array (NOEMA) large program CORE. Using NOEMA observations at 1.37 mm with an angular resolution of ~0."42 (1 400 au at 3.33 kpc), we derived the physical and chemi...
Preprint
In the disk-mediated accretion scenario for the formation of the most massive stars, gravitational instabilities in the disk can force it to fragment. We investigate the effects of inclination and spatial resolution on observable kinematics and stability of disks in high-mass star formation. We study a high-resolution 3D radiation-hydrodynamic simu...
Article
Full-text available
Context: The formation process of high-mass stars (>8 M⊙) is poorly constrained, particularly the effects of clump fragmentation creating multiple systems and the mechanism of mass accretion onto the cores. Aims: We study the fragmentation of dense gas clumps, and trace the circumstellar rotation and outflows by analyzing observations of the high-m...
Article
Full-text available
Context. The formation process of high-mass stars (>8 M⊙ ) is poorly constrained, particularly the effects of clump fragmentation creating multiple systems and the mechanism of mass accretion onto the cores. Aims. We study the fragmentation of dense gas clumps, and trace the circumstellar rotation and outflows by analyzing observations of the high-...
Preprint
Full-text available
The formation process of high-mass stars (>8M$_\odot$) is poorly constrained, particularly, the effects of clump fragmentation creating multiple systems and the mechanism of mass accretion onto the cores. We study the fragmentation of dense gas clumps, and trace the circumstellar rotation and outflows by analyzing observations of the high-mass (~50...
Article
Full-text available
Context: This study is part of the CORE project, an IRAM/NOEMA large program consisting of observations of the millimeter continuum and molecular line emission towards 20 selected high-mass star-forming regions. The goal of the program is to search for circumstellar accretion disks, study the fragmentation process of molecular clumps, and investiga...
Article
Full-text available
We present the highest angular resolution (∼20 × 15 mas–44 × 33 au) Atacama Large Millimeter/sub-millimeter Array (ALMA) observations that are currently possible of the proto-O-star G17.64+0.16 in Band 6. The Cycle 5 observations with baselines out to 16 km probe scales < 50 au and reveal the rotating disc around G17.64+0.16, a massive forming O-ty...
Preprint
Full-text available
We present the highest angular resolution (20x15mas - 44x33au) Atacama Large Millimeter/sub-millimeter Array (ALMA) observations currently possible of the proto-O-star G17.64+0.16 in Band 6. The Cycle 5 observations with baselines out to 16km probes scales <50au and reveal the rotating disc around G17.64+0.16, a massive forming O-type star. The dis...
Article
Context. This study is part of the CORE project, an IRAM/NOEMA large program consisting of observations of the millimeter continuum and molecular line emission towards 20 selected high-mass star-forming regions. The goal of the program is to search for circumstellar accretion disks, study the fragmentation process of molecular clumps, and investiga...
Preprint
Full-text available
This study is part of the project ``CORE'', an IRAM/NOEMA large program consisting of observations of the millimeter continuum and molecular line emission towards 20 selected high-mass star forming regions. We focus on IRAS23385+6053, which is believed to be the least evolved source of the CORE sample. The observations were performed at ~1.4 mm and...
Article
We present high angular resolution (~0.2″) continuum and molecular emission line Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of G17.64+0.16 in Band 6 (220−230 GHz) taken as part of a campaign in search of circumstellar discs around (proto)-O-stars. At a resolution of ~400 au the main continuum core is essentially unresolved an...
Article
Full-text available
Context. The hierarchical process of star formation has so far mostly been studied on scales from thousands of au to parsecs, but the smaller sub-1000 au scales of high-mass star formation are still largely unexplored in the submillimeter regime. Aims. We aim to resolve the dust and gas emission at the highest spatial resolution to study the physic...
Article
Full-text available
Context. The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the most luminous objects have yet to be comprehensively characterised. Aims. We study the fragmentation and kinematics of the high-mass star-forming region W3(H 2 O), as part of the IRAM NOrthern Extended Millimeter Array...
Preprint
We present high angular resolution 0.2 arcsec continuum and molecular emission line Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of G17.64+0.16 in Band 6 (220GHz) taken as part of a campaign in search of circumstellar discs around (proto)-O-stars. At a resolution of 400au the main continuum core is essentially unresolved and is...
Article
We present high angular resolution (~0.2″) continuum and molecular emission line Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of G17.64+0.16 in Band 6 (220-230 GHz) taken as part of a campaign in search of circumstellar discs around (proto)-O-stars. At a resolution of ~400 au the main continuum core is essentially unresolved an...
Article
Full-text available
Context: High-mass stars form in clusters, but neither the early fragmentation processes nor the detailed physical processes leading to the most massive stars are well understood. Aims: We aim to understand the fragmentation, as well as the disk formation, outflow generation, and chemical processes during high-mass star formation on spatial scales...
Article
Context: G24.78+0.08 is a well known high-mass star-forming region, where several molecular cores harboring OB young stellar objects are found inside a clump of size ≈1 pc. This article focuses on the most prominent of these cores, A1, where an intense hypercompact (HC) HII region has been discovered by previous observations. Aims: Our aim is to de...
Preprint
Full-text available
The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the most luminous objects have yet to be comprehensively characterised. Using the IRAM NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30-m telescope, the CORE survey has obtained high-resolution observations of 20 well-kno...
Article
Context. High-mass stars form in clusters, but neither the early fragmentation processes nor the detailed physical processes leading to the most massive stars are well understood. Aims. We aim to understand the fragmentation, as well as the disk formation, outflow generation, and chemical processes during high-mass star formation on spatial scales...
Preprint
Full-text available
Aims: We aim to understand the fragmentation as well as the disk formation, outflow generation and chemical processes during high-mass star formation on spatial scales of individual cores. Methods: Using the IRAM Northern Extended Millimeter Array (NOEMA) in combination with the 30m telescope, we have observed in the IRAM large program CORE the 1.3...
Article
Full-text available
The nearby open cluster NGC 752 presents a rare opportunity to study stellar properties at ages >1 Gyr. However, constructing a membership catalog for it is challenging; most surveys have been limited to identifying its giants and dwarf members earlier than mid-K. We supplement past membership catalogs with candidates selected with updated photomet...
Article
Full-text available
Context. G24.78+0.08 is a well known high-mass star-forming region, where several molecular cores harboring OB young stellar objects are found inside a clump of size ≈1 pc. This article focuses on the most prominent of these cores, A1, where an intense hypercompact (HC) H II region has been discovered by previous observations. Aims. Our aim is to d...