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M. Kuhn

Publications and source records attributed to M. Kuhn.

10 recordsLinked to original sources
arXiv2024

Gaia23bab : a new EXor

On March 6 2023, the Gaia telescope has alerted a 2-magnitude burst from Gaia23bab, a Young Stellar Object in the Galactic plane. We observed Gaia23bab with the Large Binocular Telescope obtaining optical and near-infrared spectra close in time to the peak of the burst, and collected all public multi-band photometry to reconstruct the historical light curve. This latter shows three bursts in ten years (2013, 2017 and 2023), whose duration and amplitude are typical of EXor variables. We estimate that, due to the bursts, the mass accumulated on the star is about twice greater than if the source had remained quiescent for the same period of time. Photometric analysis indicates that Gaia23bab is a Class,II source with age < 1 Myr, spectral type G3-K0, stellar luminosity 4.0 L_sun, and mass 1.6 M_sun. The optical/near infrared spectrum is rich in emission lines. From the analysis of these lines we measured the accretion luminosity and the mass accretion rate L_acc(burst)=3.7 L_sun, M_acc(burst) 2.0 10 $^(-7) M_sun/yr, consistent with those of EXors. More generally, we derive the relationships between accretion and stellar parameters in a sample of EXors. We find that, when in burst, the accretion parameters become almost independent of the stellar parameters and that EXors, even in quiescence, are more efficient than classical T Tauri stars in assembling mass.

astro-ph.SR↗
arXiv2019

Astro2020 Science White Paper: The Next Decade of Astroinformatics and Astrostatistics

Over the past century, major advances in astronomy and astrophysics have been largely driven by improvements in instrumentation and data collection. With the amassing of high quality data from new telescopes, and especially with the advent of deep and large astronomical surveys, it is becoming clear that future advances will also rely heavily on how those data are analyzed and interpreted. New methodologies derived from advances in statistics, computer science, and machine learning are beginning to be employed in sophisticated investigations that are not only bringing forth new discoveries, but are placing them on a solid footing. Progress in wide-field sky surveys, interferometric imaging, precision cosmology, exoplanet detection and characterization, and many subfields of stellar, Galactic and extragalactic astronomy, has resulted in complex data analysis challenges that must be solved to perform scientific inference. Research in astrostatistics and astroinformatics will be necessary to develop the state-of-the-art methodology needed in astronomy. Overcoming these challenges requires dedicated, interdisciplinary research. We recommend: (1) increasing funding for interdisciplinary projects in astrostatistics and astroinformatics; (2) dedicating space and time at conferences for interdisciplinary research and promotion; (3) developing sustainable funding for long-term astrostatisics appointments; and (4) funding infrastructure development for data archives and archive support, state-of-the-art algorithms, and efficient computing.

astro-ph.IM↗
arXiv2018

Magic Numbers for Packing Adamantane in Helium Droplets: Cluster Cations, Dications and Trications

We report the first observation of cations, dications and trications of large clusters of adamantane. Cluster formation was initiated near 0 K in helium droplets and ionization was achieved with one or more collisions with energetic He species (He$^{\star}$, He$^{+}$ or He$^{\star}$$^{-}$). The occurrence of Coulomb explosion appeared to discriminate against the formation of small multiply charged clusters. High resolution mass spectrometry revealed the presence of "magic number" m/z peaks that can be attributed to the packing of adamantane molecules into cluster structures of special stability involving preferred arrangements of these molecules. These abundance anomalies were seen to be independent of charge state. While some dehydrogenation of adamantane and its clusters was seen as well, no major transformations into adamantoids or microdiamonds were observed.

physics.atm-clus↗
arXiv2018

Electron-induced chemistry in imidazole clusters embedded in helium nanodroplets

Electron-induced chemistry in imidazole (IMI) clusters embedded in helium nanodroplets (with an average size of 2$\times$10$^5$ He atoms) has been investigated with high-resoluton time-of-flight mass spectrometry. The formation of both, negative and positive, ions was monitored as a function of the cluster size n. In both ion spectra a clear series of peaks with IMI cluster sizes up to at least 25 are observed. While the anions are formed by collisions of IMI$_n$ with He$^\star$$^{-}$, the cations are formed through ionization of IMI$_n$ by He$^{+}$ as the measured onset for the cation formation is observed at 24.6 eV (ionization energy of He). The most abundant series of anions are dehydrogenated anions IMI$_{n-1}$(IMI-H)$^{-}$, while other anion series are IMI clusters involving CN and C$_2$H$_4$ moieties. The formation of cations is dominated by the protonated cluster ions IMI$_n$H$^{+}$, while the intensity of parent cluster cations IMI$_n$$^{+}$ is also observed preferentially for the small cluster size n. The observation of series of cluster cations [IMI$_n$CH$_3$]$^{+}$ suggests either CH$_3$$^{+}$ cation to be solvated by n neutral IMI molecules, or the electron-induced chemistry has led to the formation of protonated methyl-imidazole solvated by (n-1) neutral IMI molecules.

physics.atm-clus↗
arXiv2016

Young Stellar Clusters Containing Massive Young Stellar Objects in the VVV Survey

The purpose of this research is to study the connection of global properties of eight young stellar clusters projected in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey disk area and their young stellar object population. The analysis in based on the combination of spectroscopic parallax-based reddening and distance determinations with main sequence and pre-main sequence ishochrone fitting to determine the basic parameters (reddening, age, distance) of the sample clusters. The lower mass limit estimations show that all clusters are low or intermediate mass (between 110 and 1800 Mo), the slope Gamma of the obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. On the other hand, the young stellar objects in the surrounding cluster's fields are classified by low resolution spectra, spectral energy distribution fit with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed young stellar objects (except one) are found to be massive (more than 8 Mo). Using VVV and GLIMPSE color-color cuts we have selected a large number of new young stellar object candidates, which are checked for variability and 57% are found to show at least low-amplitude variations. In few cases it was possible to distinguish between YSO and AGB classification on the basis of the light curves.

astro-ph.GA↗
arXiv2016

Ultra-Low-Temperature Reactions of Carbon Atoms with Hydrogen Molecules

The reactions of carbon atoms with dihydrogen have been investigated in liquid helium droplets at $T$ = 0.37 K. A calorimetric technique was applied to monitor the energy released in the reaction. The barrierless reaction between a single carbon atom and a single dihydrogen molecule was detected. Reactions between dihydrogen clusters and carbon atoms have been studied by high-resolution mass spectrometry. The formation of hydrocarbon cations of the type C$_m$H$_n^+$, with $m$ = 1-4 and $n$ = 1-15 was observed. With enhanced concentration of dihydrogen, the mass spectra demonstrated the main "magic" peak assigned to the CH$_5^+$ cation. A simple formation pathway and the high stability of this cation suggest its high abundance in the interstellar medium.

astro-ph.GA↗
arXiv2016

Massive open star clusters using the VVV survey V. Young clusters with an OB stellar population

The ESO public survey VISTA Variables in the Vía Láctea (VVV) has contributed with deep multi-epoch photometry of the Galactic bulge and the adjacent part of the disk over 526 square degrees. More than a hundred cluster candidates have been reported thanks to this survey. We present the fifth article in a series of papers focused on young and massive clusters discovered in the VVV survey. In this paper, we present the physical characterization of five clusters with a spectroscopically confirmed OB-type stellar population. To characterize the clusters, we used near-infrared photometry ($J$, $H,$ and $K_S$) from the VVV survey and near-infrared $K$-band spectroscopy from ISAAC at VLT, following the methodology presented in the previous articles of the series. All clusters in our sample are very young (ages between 1-20 Myr), and their total mass are between $(1.07^{+0.40}_{-0.30})\cdot10^2$ $M_{\odot}$ and $(4.17^{+4.15}_{-2.08})\cdot10^3$ $M_{\odot}$. We observed a relation between the clusters total mass $M_{ecl}$ and the mass of their most massive stellar member $m_{max}$, even for clusters with an age $<$ 10 Myr.

astro-ph.SR↗
arXiv2015

Massive open star clusters using the VVV survey IV. WR 62-2, a new very massive star in the core of the VVV CL041 cluster

Context The ESO Public Survey VISTA Variables in the Vía Láctea (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims We present the fourth article in a series of papers focussed on young and massive clusters discovered in the VVV survey. This article is dedicated to the cluster VVV CL041, which contains a new very massive star candidate, WR 62-2. Methods Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters (distance, reddening, mass, age) of VVV CL041. Results We confirm that the cluster VVV CL041 is a young (less than 4 Myrs) and massive (3 +/- 2 x 10^3 Msol) cluster, and not a simple asterism. It is located at a distance of 4.2 +/- 0.9 kpc, and its reddening is A_V = 8.0 +/- 0.2 mag, which is slightly lower than the average for the young clusters towards the centre of the Galaxy. Spectral analysis shows that the most luminous star of the cluster, of the WN8h spectral type, is a candidate to have an initial mass larger than 100 Msol.

astro-ph.SR↗
arXiv2015

A not so massive cluster hosting a very massive star

We present the first physical characterization of the young open cluster VVV CL041. We spectroscopically observed the cluster main-sequence stellar population and a very-massive star candidate: WR62-2. CMFGEN modeling to our near-infrared spectra indicates that WR62-2 is a very luminous (10$^{6.4\pm0.2} L_{\odot}$) and massive ($\sim80 M_{\odot}$) star.

astro-ph.SR↗