scholarly journals The Substellar Members of the Pleiades

2003 ◽  
Vol 211 ◽  
pp. 181-182
Author(s):  
Paul D. Dobbie ◽  
Richard F. Jameson ◽  
Samantha L. Osborne ◽  
Simon T. Hodgkin ◽  
David J. Pinfield
Keyword(s):  
Dark Matter ◽  
Spatial Distribution ◽  
Power Law ◽  
Spatial Model ◽  
Total Mass ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Core Radius ◽  
Brown Dwarf ◽  
Limited Sample

We have compiled the largest magnitude limited sample of candidate substellar Pleiads to date. We fit King profiles to their spatial distribution to determine the Pleiades brown dwarf core radius to be Subsequently we have used our improved spatial model to place stringent limits on the shape of the cluster mass function across and below the stellar/substellar regime. We find this to be a power law with index α = 0.41±0.08 (0.3M⊙ ≥M≥ 0.035M⊙). Extrapolation of this mass function to M= 0.012M⊙ indicates that brown dwarfs contribute only ~ 2% to the total mass of the cluster hence we conclude that brown dwarfs do not contribute significantly to disk dark matter.

DARK MATTER IN THE GALAXY

1994 ◽  
Vol 03 (supp01) ◽  
pp. 53-61
Author(s):  
ROSEMARY F.G. WYSE
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Galactic Disk ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
Vertical Force ◽  
Chemical Abundances ◽  
Stellar Objects

I will first review the evidence that our Milky Way Galaxy contains a substantial amount of dark matter, and what is known about the spatial distribution of this material, from rotation curve decompositions and from analysis of the vertical force law in the solar neighborhood. All data are consistent with no significant unidentified material in the Galactic disk, requiring that the dark matter be in a spatially-extended distribution. Brown dwarfs, or sub-stellar objects, are often discussed as possible dark-matter candidates, especially in view of the implication from nucleosynthesis calculations that dark baryons exist. The somewhat discour-aging status of recent searches for brown dwarfs is reviewed, together with present understanding of the low-mass stellar initial mass function. I discuss a long-term survey of the motions and chemical abundances of Galactic stars which will provide constraints on the Galactic potential well and the history of Galaxy formation.

scholarly journals Estimating Finite Source Effects in Microlensing Events due to Free-Floating Planets with the Euclid Survey

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Lindita Hamolli ◽  
Mimoza Hafizi ◽  
Francesco De Paolis ◽  
Achille A. Nucita
Keyword(s):  
Spatial Distribution ◽  
Power Law ◽  
Mass Function ◽  
Physical Parameters ◽  
Galactic Bulge ◽  
Source Effect ◽  
Source Effects ◽  
Function Index ◽  
Finite Source ◽  
Einstein Radius

In recent years free-floating planets (FFPs) have drawn a great interest among astrophysicists. Gravitational microlensing is a unique and exclusive method for their investigation which may allow obtaining precious information about their mass and spatial distribution. The planned Euclid space-based observatory will be able to detect a substantial number of microlensing events caused by FFPs towards the Galactic bulge. Making use of a synthetic population algorithm, we investigate the possibility of detecting finite source effects in simulated microlensing events due to FFPs. We find a significant efficiency for finite source effect detection that turns out to be between 20% and 40% for a FFP power law mass function index in the range [0.9, 1.6]. For many of such events it will also be possible to measure the angular Einstein radius and therefore constrain the lens physical parameters. These kinds of observations will also offer a unique possibility to investigate the photosphere and atmosphere of Galactic bulge stars.

scholarly journals 6.12. Microlensing and dynamics of the Galactic bulge

1998 ◽  
Vol 184 ◽  
pp. 285-286
Author(s):  
H.S. Zhao
Keyword(s):  
Spatial Distribution ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Dynamical Model ◽  
Galactic Bulge ◽  
Galactic Disc

Microlensing (μ—lensing) towards the bulge started out as a unique technique of detecting dark objects in the Galactic disc (brown dwarfs) by measuring a rare transient brightening of one star among millions of stars in the Galactic bulge (Paczyński 1991). More than 200 events have been detected towards the Bulge since 1993 by the DUO, MACHO, OGLE etc. survey teams. But where are the lenses? Are they truly dark objects or merely faint stars? I show the results on the mass function, spatial distribution and dynamics of these observed lenses based on a dynamical model of the Galactic bar.

scholarly journals Brown dwarfs in the Pleiades: spatial distribution and mass function

2002 ◽  
Vol 335 (3) ◽  
pp. 853-863 ◽  
Author(s):  
R. F. Jameson ◽  
P. D. Dobbie ◽  
S. T. Hodgkin ◽  
D. J. Pinfield
Keyword(s):  
Spatial Distribution ◽  
Brown Dwarfs ◽  
Mass Function

scholarly journals The Brown Dwarf Kinematics Project (BDKP). V. Radial and Rotational Velocities of T Dwarfs from Keck/NIRSPEC High-resolution Spectroscopy

2021 ◽  
Vol 257 (2) ◽  
pp. 45
Author(s):  
Chih-Chun Hsu ◽  
Adam J. Burgasser ◽  
Christopher A. Theissen ◽  
Christopher R. Gelino ◽  
Jessica L. Birky ◽  
...  
Keyword(s):  
Main Sequence ◽  
Formation Rate ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Radial Velocities ◽  
High Resolution Spectroscopy ◽  
Brown Dwarf ◽  
M Dwarfs ◽  
L Dwarfs ◽  
Orbital Periods

Abstract We report multiepoch radial velocities, rotational velocities, and atmospheric parameters for 37 T-type brown dwarfs observed with Keck/NIRSPEC. Using a Markov Chain Monte Carlo forward-modeling method, we achieve median precisions of 0.5 and 0.9 km s−1 for radial and rotational velocities, respectively. All of the T dwarfs in our sample are thin-disk brown dwarfs. We confirm previously reported moving group associations for four T dwarfs. However, the lack of spectral indicators of youth in two of these sources suggests that these are chance alignments. We confirm two previously unresolved binary candidates, the T0+T4.5 2MASS J11061197+2754225 and the L7+T3.5 2MASS J21265916+7617440, with orbital periods of 4 and 12 yr, respectively. We find a kinematic age of 3.5 ± 0.3 Gyr for local T dwarfs, consistent with nearby late M dwarfs (4.1 ± 0.3 Gyr). Removal of thick-disk L dwarfs in the local ultracool dwarf sample gives a similar age for L dwarfs (4.2 ± 0.3 Gyr), largely resolving the local L dwarf age anomaly. The kinematic ages of local late M, L, and T dwarfs can be accurately reproduced with population simulations incorporating standard assumptions of the mass function, star formation rate, and brown dwarf evolutionary models. A kinematic dispersion break is found at the L4–L6 subtypes, likely reflecting the terminus of the stellar main sequence. We provide a compilation of precise radial velocities for 172 late M, L, and T dwarfs within ∼20 pc of the Sun.

scholarly journals The Central Dark Matter Fraction of Massive Early-Type Galaxies

2022 ◽  
Vol 8 ◽  
Author(s):  
C. Tortora ◽  
N. R. Napolitano
Keyword(s):  
Dark Matter ◽  
Total Mass ◽  
Mass Density ◽  
Mass Function ◽  
Initial Mass Function ◽  
Early Type ◽  
Galaxy Model ◽  
Stellar Initial Mass Function ◽  
Evolution With Time

Dark matter (DM) is predicted to be the dominant mass component in galaxies. In the central region of early-type galaxies it is expected to account for a large amount of the total mass, although the stellar mass should still represent the majority of the mass budget, depending on the stellar initial mass function (IMF). We discuss latest results on the DM fraction and mean DM density for local galaxies and explore their evolution with redshifts in the last 8 Gyr of the cosmic history. We compare these results with expectations from the ΛCDM model and discuss the role of the IMF and galaxy model through the central total mass density slope. We finally present future perspectives offered by next-generation instruments/surveys (Rubin/LSST, Euclid, CSST, WEAVE, 4MOST, and DESI), which will provide the unique chance to measure the DM evolution with time for an unprecedented number of galaxies and constrain their evolutionary scenario.

scholarly journals The Next Generation Sky Survey and the Quest for Cooler Brown Dwarfs

2003 ◽  
Vol 211 ◽  
pp. 497-504 ◽  
Author(s):  
J. Davy Kirkpatrick
Keyword(s):  
Brown Dwarfs ◽  
Mass Function ◽  
Solar Neighborhood ◽  
The Sun ◽  
Next Generation ◽  
Brown Dwarf ◽  
Field Mass ◽  
The Earth ◽  
Luminosity Functions ◽  
Sky Survey

The Next Generation Sky Survey (NGSS) is a proposed NASA MIDEX mission to map the entire sky in four infrared bandpasses – 3.5, 4.7, 12, and 23 μm. The seven-month mission will use a 50-cm telescope and four-channel imager to survey the sky from a circular orbit above the Earth. Expected sensitivities will be half a million times that of COBE/DIRBE at 3.5 and 4.7 μm and a thousand times that of IRAS at 12 and 23 μm. NGSS will be particularly sensitive to brown dwarfs cooler than those presently known. Deep absorption in the methane fundamental band at 3.3 μm and a predicted 5-μm overluminosity will produce uniquely red 3.5-to-4.7 μm colors for such objects. For a limiting volume of 25 pc, NGSS will completely inventory the Solar Neighborhood for brown dwarfs as cool as Gl 229B. At 10 pc, the census will be complete to 500 K. Assuming a field mass function with α = 1, there could be one or more brown dwarfs warmer than 150 K lying closer to the Sun than Proxima Centauri and detectable primarily at NGSS wavelengths. NGSS will enable estimates of the brown dwarf mass and luminosity functions to very cool temperatures and will provide both astrometric references and science targets for NGST.

scholarly journals Cusp or core? Revisiting the globular cluster timing problem in Fornax

2019 ◽  
Vol 491 (3) ◽  
pp. 3336-3342 ◽  
Author(s):  
Noah Meadows ◽  
Julio F Navarro ◽  
Isabel Santos-Santos ◽  
Alejandro Benítez-Llambay ◽  
Carlos Frenk
Keyword(s):  
Spatial Distribution ◽  
Globular Cluster ◽  
Total Mass ◽  
Effective Radius ◽  
Constant Density ◽  
Core Radius ◽  
Dynamical Friction ◽  
The Core ◽  
Spatially Extended ◽  
Projected Distance

ABSTRACT We use N-body simulations to revisit the globular cluster (GC) ‘timing problem’ in the Fornax dwarf spheroidal (dSph). In agreement with earlier work, we find that, due to dynamical friction, GCs sink to the centre of dark matter haloes with a cuspy inner density profile but ‘stall’ at roughly 1/3 of the core radius (rcore) in haloes with constant-density cores. The time-scales to sink or stall depend strongly on the mass of the GC and on the initial orbital radius, but are essentially the same for either cuspy (Navarro–Frenk–White) or cored haloes normalized to have the same total mass within rcore. Arguing against a cusp on the basis that GCs have not sunk to the centre is thus no different from arguing against a core, unless all clusters are today at $\sim(1/3)\,r_{\rm core}$. This would imply a core radius exceeding ∼3 kpc, much larger than seems plausible in any core-formation scenario. (The average projected distance of Fornax GCs is 〈RGC, Fnx〉 ∼ 1 kpc and its effective radius is ∼700 pc.) A simpler explanation is that Fornax GCs have only been modestly affected by dynamical friction, as expected if clusters started orbiting at initial radii of the order of ∼1–2 kpc, just outside Fornax’s present-day half-light radius but well within the tidal radius imprinted by Galactic tides. This is not entirely unexpected. Fornax GCs are significantly older and more metal-poor than most Fornax stars, and such populations in dSphs tend to be more spatially extended than their younger and more metal-rich counterparts. Contrary to some earlier claims, our simulations further suggest that GCs do not truly ‘stall’ at $\sim 0.3\, r_{\rm core}$, but rather continue decaying towards the centre, albeit at reduced rates. We conclude that dismissing the presence of a cusp in Fornax based on the spatial distribution of its GC population is unwarranted.

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