scholarly journals Monoceros OB4: a new association in Gaia DR2

2021 ◽  
Vol 504 (1) ◽  
pp. L17-L21
Author(s):  
P S Teixeira ◽  
J Alves ◽  
A Sicilia-Aguilar ◽  
A Hacar ◽  
A Scholz
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
Line Of Sight ◽  
Young Population ◽  
Proper Motions ◽  
Star Formation Region ◽  
General Line ◽  
New Association ◽  
Cloud Complex ◽  
Gaia Dr2

ABSTRACT We use Gaia DR2 data to survey the classic Monoceros OB1 region and look for the existence of a dispersed young population, co-moving with the cloud complex. An analysis of the distribution of proper motions reveals a 20–30 Myr association of young stars, about 300–400 pc away from the far side of the Mon OB1 complex, along the same general line of sight. We characterize the new association, Monoceros OB4, and estimate it contains between 1400 and 2500 stars, assuming a standard initial mass function, putting it on par in size with NGC 2264. We find from the internal proper motions that Mon OB4 is unbound and expanding. Our results seem to unveil a larger and more complex Monoceros star formation region, suggesting an elongated arrangement that seems to be at least 300 × 60 pc.

scholarly journals The Stellar Content of SCO OB2

1987 ◽  
Vol 115 ◽  
pp. 205-206
Author(s):  
Eugène de Geus ◽  
Tim de Zeeuw
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Mass Function ◽  
Initial Mass Function ◽  
Apparent Magnitude ◽  
Proper Motions ◽  
Stellar Content ◽  
Angular Extent ◽  
Motion Measurements ◽  
Ob Associations

The study of the stellar content of nearby OB associations is important for understanding the Initial Mass Function, the study of differential age effects and for a better knowledge of the ambient radiation field, which plays an important role in the interpretation of measurements of gas and dust. Unfortunately, even for the nearest OB associations membership is known very poorly. In most cases no main sequence members of spectral type later than B5 are known. Membership determination using colour-magnitude diagrams suffers from the large intrinsic distance spread. The large angular extent on the sky of most associations makes proper motion measurements difficult to compare because of problems connecting photographic plates with different plate centers. In order to remedy this situation a consortium called SPECTER has been formed at Leiden Observatory. It has been granted observing time on the HIPPARCOS satellite for measuring proper motions of about 10000 candidate members of the OB associations within 600 pc of the Sun. Candidates were selected according to spectral type (not later than F8) apparent magnitude, and location. In anticipation of the HIPPARCOS results, SPECTER will gather a variety of other data. We have nearly completed a program aimed at obtaining VBLUW-photometry (Lub and Pel 1977) of all candidate stars visible from the Southern Hemisphere. Here we discuss the preliminary results for the association Sco OB2.

scholarly journals The luminosity function of nearby thick-disk sub-dwarfs

2007 ◽  
Vol 3 (S248) ◽  
pp. 484-485
Author(s):  
M. I. Arifyanto
Keyword(s):  
Luminosity Function ◽  
Absolute Magnitude ◽  
Mass Function ◽  
Initial Mass Function ◽  
Radial Velocities ◽  
Thick Disk ◽  
Initial Mass ◽  
Proper Motions ◽  
Dwarf Stars ◽  
Magnitude Range

AbstractWe derived the luminosity function of thick disk using V/Vmax method for nearby sub-dwarf stars based on the sample stars of Carney et al. (1994). Hipparcos parallaxes and proper motions and Tycho2 proper motions were combined with radial velocities and metallicities from CLLA. We found that the luminosity function in the absolute magnitude range MV = 4–6 mag agree well with the luminosity function derived from the initial mass function (Reyle & Robin 2001).

scholarly journals Kinematics of RR Lyrae stars in the Galactic bulge with OGLE-IV and Gaia DR2

2020 ◽  
Vol 498 (4) ◽  
pp. 5629-5642
Author(s):  
Hangci Du ◽  
Shude Mao ◽  
E Athanassoula ◽  
Juntai Shen ◽  
Pawel Pietrukowicz
Keyword(s):  
Velocity Dispersion ◽  
Line Of Sight ◽  
Proper Motions ◽  
Galactic Bulge ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Halo Stars ◽  
Central Regions ◽  
Lyrae Stars ◽  
Gaia Dr2

ABSTRACT We analyse the kinematics and spatial distribution of 15 599 fundamental-mode RR Lyrae (RRL) stars in the Milky Way bulge by combining OGLE-IV photometric data and Gaia DR2 proper motions. We show that the longitudinal proper motions and the line-of-sight velocities can give similar results for the rotation in the Galactic central regions. The angular velocity of bulge RRLs is found to be around 35 km s−1 kpc−1, significantly smaller than that for the majority of bulge stars (50–60 km s−1 kpc−1); bulge RRLs have larger velocity dispersion (120–140 km s−1) than younger stars. The dependence of the kinematics of the bulge RRLs on their metallicities is shown by their rotation curves and spatial distributions. Metal-poor RRLs ([Fe/H]<−1) show a smaller bar angle than metal-rich ones. We also find clues suggesting that RRLs in the bulge are not dominated by halo stars. These results might explain some previous conflicting results over bulge RRLs and help understand the chemodynamical evolution of the Galactic bulge.

scholarly journals The star formation region NGC 6530: Distance, ages and initial mass function

2005 ◽  
Vol 430 (3) ◽  
pp. 941-957 ◽  
Author(s):  
L. Prisinzano ◽  
F. Damiani ◽  
G. Micela ◽  
S. Sciortino
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Formation Region ◽  
Formation Region

Low‐Mass Star Formation and the Initial Mass Function in IC 348

1998 ◽  
Vol 508 (1) ◽  
pp. 347-369 ◽  
Author(s):  
K. L. Luhman ◽  
G. H. Rieke ◽  
C. J. Lada ◽  
E. A. Lada
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Mass Star ◽  
Low Mass

scholarly journals Very Low-Luminosity Objects in Star-Forming Regions

1998 ◽  
Vol 11 (1) ◽  
pp. 423-424
Author(s):  
Motohide Tamura ◽  
Yoichi Itoh ◽  
Yumiko Oasa ◽  
Alan Tokunaga ◽  
Koji Sugitani
Keyword(s):  
Brown Dwarfs ◽  
Mass Function ◽  
T Tauri Stars ◽  
Initial Mass Function ◽  
Formation Mechanisms ◽  
Star Forming ◽  
Star Forming Regions ◽  
T Tauri ◽  
Low Mass ◽  
Stellar Sources

Abstract In order to tackle the problems of low-mass end of the initial mass function (IMF) in star-forming regions and the formation mechanisms of brown dwarfs, we have conducted deep infrared surveys of nearby molecular clouds. We have found a significant population of very low-luminosity sources with IR excesses in the Taurus cloud and the Chamaeleon cloud core regions whose extinction corrected J magnitudes are 3 to 8 mag fainter than those of typical T Tauri stars in the same cloud. Some of them are associated with even fainter companions. Follow-up IR spectroscopy has confirmed for the selected sources that their photospheric temperature is around 2000 to 3000 K. Thus, these very low-luminosity young stellar sources are most likely very low-mass T Tauri stars, and some of them might even be young brown dwarfs.

scholarly journals 2D kinematics of massive stars near the Galactic Centre

2020 ◽  
Vol 500 (3) ◽  
pp. 3213-3239
Author(s):  
Mattia Libralato ◽  
Daniel J Lennon ◽  
Andrea Bellini ◽  
Roeland van der Marel ◽  
Simon J Clark ◽  
...  
Keyword(s):  
Moving Objects ◽  
Hubble Space Telescope ◽  
Massive Stars ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Harsh Environment ◽  
Proper Motions ◽  
Sgr A ◽  
Better Than ◽  
Rule Out

ABSTRACT The presence of massive stars (MSs) in the region close to the Galactic Centre (GC) poses several questions about their origin. The harsh environment of the GC favours specific formation scenarios, each of which should imprint characteristic kinematic features on the MSs. We present a 2D kinematic analysis of MSs in a GC region surrounding Sgr A* based on high-precision proper motions obtained with the Hubble Space Telescope. Thanks to a careful data reduction, well-measured bright stars in our proper-motion catalogues have errors better than 0.5 mas yr−1. We discuss the absolute motion of the MSs in the field and their motion relative to Sgr A*, the Arches, and the Quintuplet. For the majority of the MSs, we rule out any distance further than 3–4 kpc from Sgr A* using only kinematic arguments. If their membership to the GC is confirmed, most of the isolated MSs are likely not associated with either the Arches or Quintuplet clusters or Sgr A*. Only a few MSs have proper motions, suggesting that they are likely members of the Arches cluster, in agreement with previous spectroscopic results. Line-of-sight radial velocities and distances are required to shed further light on the origin of most of these massive objects. We also present an analysis of other fast-moving objects in the GC region, finding no clear excess of high-velocity escaping stars. We make our astro-photometric catalogues publicly available.

Recovering the star formation history of galaxies through spectral fitting: Current challenges

2019 ◽  
Vol 15 (S359) ◽  
pp. 386-390
Author(s):  
Lucimara P. Martins
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Stellar Spectra ◽  
Spectral Fitting ◽  
Formation History ◽  
History Of ◽  
Nearby Galaxies ◽  
Extract Information

AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.

scholarly journals Do ultracompact dwarf galaxies form monolithically or as merged star cluster complexes?

2021 ◽  
Vol 502 (4) ◽  
pp. 5185-5199
Author(s):  
Hamidreza Mahani ◽  
Akram Hasani Zonoozi ◽  
Hosein Haghi ◽  
Tereza Jeřábková ◽  
Pavel Kroupa ◽  
...  
Keyword(s):  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Mass Function ◽  
Star Cluster ◽  
Initial Mass Function ◽  
Central Mass ◽  
Cluster Complexes ◽  
V Band ◽  
Stellar Masses ◽  
The Imf

ABSTRACT Some ultracompact dwarf galaxies (UCDs) have elevated observed dynamical V-band mass-to-light (M/LV) ratios with respect to what is expected from their stellar populations assuming a canonical initial mass function (IMF). Observations have also revealed the presence of a compact dark object in the centres of several UCDs, having a mass of a few to 15 per cent of the present-day stellar mass of the UCD. This central mass concentration has typically been interpreted as a supermassive black hole, but can in principle also be a subcluster of stellar remnants. We explore the following two formation scenarios of UCDs: (i) monolithic collapse and (ii) mergers of star clusters in cluster complexes as are observed in massively starbursting regions. We explore the physical properties of the UCDs at different evolutionary stages assuming different initial stellar masses of the UCDs and the IMF being either universal or changing systematically with metallicity and density according to the integrated Galactic IMF theory. While the observed elevated M/LV ratios of the UCDs cannot be reproduced if the IMF is invariant and universal, the empirically derived IMF that varies systematically with density and metallicity shows agreement with the observations. Incorporating the UCD-mass-dependent retention fraction of dark remnants improves this agreement. In addition, we apply the results of N-body simulations to young UCDs and show that the same initial conditions describing the observed M/LV ratios reproduce the observed relation between the half-mass radii and the present-day masses of the UCDs. The findings thus suggest that the majority of UCDs that have elevated M/LV ratios could have formed monolithically with significant remnant-mass components that are centrally concentrated, while those with small M/LV values may be merged star cluster complexes.

scholarly journals Processes controlling the initial mass function: interstellar turbulence and magnetic fields

1991 ◽  
Vol 147 ◽  
pp. 407-408
Author(s):  
R. C. Fleck
Keyword(s):  
Magnetic Fields ◽  
Mass Function ◽  
Diffusion Time ◽  
Interstellar Cloud ◽  
Initial Mass Function ◽  
Mass Scaling ◽  
Interstellar Turbulence ◽  
Time Scaling ◽  
Turbulent Pressure ◽  
Low Mass

The observed flattening of the initial stellar mass function at low mass can be accounted for in terms of the different interstellar cloud size-mass scaling and different ambipolar diffusion time scaling for small, thermally-supported clouds and larger clouds supported primarily by turbulent pressure.

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