Увійти

Готові списки джерел за темами / Brown dwarfs stars / Статті в журналах

Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Brown dwarfs stars.

Статті в журналах з теми "Brown dwarfs stars"

Автор: Grafiati

Опубліковано: 16 вересня 2023

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями

Оберіть тип джерела:

Ознайомтеся з топ-50 статей у журналах для дослідження на тему "Brown dwarfs stars".

Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.

Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.

Переглядайте статті в журналах для різних дисциплін та оформлюйте правильно вашу бібліографію.

1

Majidi, Dorsa, John C. Forbes, and Abraham Loeb. "Where to Find Overmassive Brown Dwarfs: New Benchmark Systems for Binary Evolution." Astrophysical Journal 932, no. 2 (June 1, 2022): 91. http://dx.doi.org/10.3847/1538-4357/ac6501.

Повний текст джерела

Анотація:

Abstract Under the right conditions, brown dwarfs that gain enough mass late in their lives to cross the hydrogen-burning limit will not turn into low-mass stars, but rather remain essentially brown dwarf–like. While these objects, called either beige dwarfs or overmassive brown dwarfs, may exist in principle, it remains unclear exactly how they would form astrophysically. We show that accretion from AGB winds, aided by the wind Roche lobe overflow mechanism, is likely to produce a substantial population of observable overmassive brown dwarfs, though other mechanisms are still plausible. Specifically, we predict that Sun-like stars born with a massive brown dwarf companion on an orbit with a semimajor axis of order 10 au will likely produce overmassive brown dwarfs, which may be found today as companions to the donor star's remnant white dwarf. The identification and characterization of such an object would produce unique constraints on binary evolution, because there is a solid upper limit on the brown dwarf's initial mass.

Стилі APA, Harvard, Vancouver, ISO та ін.

2

Martín, Eduardo L., Mike Connelley, Dan Potter, and Hervé Bouy. "Brown Dwarf Companions to Solar-Type Stars and other Brown Dwarfs." Symposium - International Astronomical Union 213 (2004): 111–14. http://dx.doi.org/10.1017/s007418090019309x.

Повний текст джерела

Анотація:

We report on our ongoing imaging efforts to detect brown dwarfs orbiting solar-type stars and other brown dwarfs. We study the properties of brown dwarf companions as a function of primary mass. Our results indicate that the frequency of brown dwarf companions around solar-type stars for separations larger than about 40 AU is non-negligible. The frequency of brown dwarf binaries is about 20%. There is a dearth of brown dwarf binaries with separations larger than ∼20 AU. We propose that brown dwarf systems are a scaled down version of stellar systems, which probably form via triggered collapse of small molecular cores.

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Gizis, John E. "Wide Brown Dwarf Companions to Main-Sequence Stars." Symposium - International Astronomical Union 211 (2003): 281–86. http://dx.doi.org/10.1017/s0074180900210759.

Повний текст джерела

Анотація:

Many widely separated companions to main-sequence stars have been found using 2MASS. These companions include both stars and brown dwarfs. I discuss a number of systems of particular interest. Present indications are that a few percent of G dwarfs have brown dwarf companions.

Стилі APA, Harvard, Vancouver, ISO та ін.

4

Liebert, James. "Searches for Brown Dwarfs." International Astronomical Union Colloquium 147 (1994): 463–80. http://dx.doi.org/10.1017/s025292110002649x.

Повний текст джерела

Анотація:

AbstractThis review attempts a brief summary of the numerous and diverse searches for the so-called brown dwarfs, substellar objects having masses between giant planets and the lowest mass M dwarf stars.

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Bate, Matthew R. "Stellar and brown dwarf properties from numerical simulations." Proceedings of the International Astronomical Union 5, H15 (November 2009): 769–70. http://dx.doi.org/10.1017/s174392131001152x.

Повний текст джерела

Анотація:

AbstractWe review the statistical properties of stars and brown dwarfs obtained from the first hydrodynamical simulation of star cluster formation to produce more than a thousand stars and brown dwarfs while simultaneously resolving the lowest mass brown dwarfs (those with masses set by the opacity limit for fragmentation), binaries with separations down to ~ 1 AU, and discs with radii greater than ~ 10 AU. In particular, we present the eccentricity distribution of the calculation's very-low-mass and brown dwarf binaries which has not been previously published.

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Wolk, Scott J. "X-Ray Detection of Brown Dwarfs with Chandra." Symposium - International Astronomical Union 211 (2003): 447–50. http://dx.doi.org/10.1017/s0074180900211108.

Повний текст джерела

Анотація:

I review recent observations of brown dwarfs by the Chandra X-ray Observatory. These observations fall in 2 categories, young stellar clusters which contain brown dwarfs and brown dwarf candidates and directed pointings at brown dwarfs and very low mass stars. Surprisingly, there are already over 60 published detections of brown dwarfs by Chandra. A review of the X–ray characteristics shows these objects are subject to flaring and their temperatures and luminosities have a vast range which is related to age.

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Stamatellos, Dimitris, and Anthony Whitworth. "The formation of brown dwarfs in discs: Physics, numerics, and observations." Proceedings of the International Astronomical Union 6, S270 (May 2010): 223–26. http://dx.doi.org/10.1017/s174392131100041x.

Повний текст джерела

Анотація:

AbstractA large fraction of brown dwarfs and low-mass stars may form by gravitational fragmentation of relatively massive (a few 0.1 M⊙) and extended (a few hundred AU) discs around Sun-like stars. We present an ensemble of radiative hydrodynamic simulations that examine the conditions for disc fragmentation. We demonstrate that this model can explain the low-mass IMF, the brown dwarf desert, and the binary properties of low-mass stars and brown dwarfs. Observing discs that are undergoing fragmentation is possible but very improbable, as the process of disc fragmentation is short lived (discs fragment within a few thousand years).

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Persson, Carina M., Szilárd Csizmadia, Alexander J. Mustill, Malcolm Fridlund, Artie P. Hatzes, Grzegorz Nowak, Iskra Georgieva, et al. "Greening of the brown-dwarf desert." Astronomy & Astrophysics 628 (August 2019): A64. http://dx.doi.org/10.1051/0004-6361/201935505.

Повний текст джерела

Анотація:

Context. Although more than 2000 brown dwarfs have been detected to date, mainly from direct imaging, their characterisation is difficult due to their faintness and model-dependent results. In the case of transiting brown dwarfs, however, it is possible to make direct high-precision observations. Aims. Our aim is to investigate the nature and formation of brown dwarfs by adding a new well-characterised object, in terms of its mass, radius and bulk density, to the currently small sample of less than 20 transiting brown dwarfs. Methods. One brown dwarf candidate was found by the KESPRINT consortium when searching for exoplanets in the K2 space mission Campaign 16 field. We combined the K2 photometric data with a series of multicolour photometric observations, imaging, and radial velocity measurements to rule out false positive scenarios and to determine the fundamental properties of the system. Results. We report the discovery and characterisation of a transiting brown dwarf in a 5.17-day eccentric orbit around the slightly evolved F7 V star EPIC 212036875. We find a stellar mass of 1.15 ± 0.08 M⊙, a stellar radius of 1.41 ± 0.05 R⊙, and an age of 5.1 ± 0.9 Gyr. The mass and radius of the companion brown dwarf are 51 ± 2 MJ and 0.83 ± 0.03 RJ, respectively, corresponding to a mean density of 108−13+15 g cm−3. Conclusions. EPIC 212036875 b is a rare object that resides in the brown-dwarf desert. In the mass-density diagram for planets, brown dwarfs, and stars, we find that all giant planets and brown dwarfs follow the same trend from ~0.3 MJ to the turn-over to hydrogen burning stars at ~ 73 MJ. EPIC 212036875 b falls close to the theoretical model for mature H/He dominated objects in this diagram as determined by interior structure models. We argue that EPIC 212036875 b formed via gravitational disc instabilities in the outer part of the disc, followed by a quick migration. Orbital tidal circularisation may have started early in its history for a brief period when the brown dwarf’s radius was larger. The lack of spin–orbit synchronisation points to a weak stellar dissipation parameter (Q⋆′ ≳ 108), which implies a circularisation timescale of ≳23 Gyr, or suggests an interaction between the magnetic and tidal forces of the star and the brown dwarf.

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Pearson, Samuel, Aleks Scholz, Paula S. Teixeira, Koraljka Mužić, and Víctor Almendros-Abad. "The first spectroscopically confirmed brown dwarfs in NGC 2264." Monthly Notices of the Royal Astronomical Society 507, no. 3 (August 23, 2021): 4074–85. http://dx.doi.org/10.1093/mnras/stab2394.

Повний текст джерела

Анотація:

ABSTRACT We present spectroscopic follow-up observations of 68 red, faint candidates from our multi-epoch, multiwavelength, previously published survey of NGC 2264. Using near-infrared spectra from VLT/KMOS, we measure spectral types and extinction for 32 young low-mass sources. We confirm 13 as brown dwarfs in NGC 2264, with spectral types between M6 and M8, corresponding to masses between 0.02 and 0.08 M⊙. These are the first spectroscopically confirmed brown dwarfs in this benchmark cluster. 19 more objects are found to be young M-type stars of NGC 2264 with masses of 0.08–0.3 M⊙. 7 of the confirmed brown dwarfs as well as 15 of the M-stars have IR excess caused by a disc. Comparing with isochrones, the typical age of the confirmed brown dwarfs is <0.5–5 Myr. More than half of the newly identified brown dwarfs and very low-mass stars have ages <0.5 Myr, significantly younger than the bulk of the known cluster population. Based on the success rate of our spectroscopic follow-up, we estimate that NGC 2264 hosts 200–600 brown dwarfs in total (in the given mass range). This would correspond to a star-to-brown dwarf ratio between 2.5:1 and 7.5:1. We determine the slope of the substellar mass function as $\alpha = 0.43^{+0.41}_{-0.56}$; these values are consistent with those measured for other young clusters. This points to a uniform substellar mass function across all star-forming environments.

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Baraffe, I., and F. Allard. "Atmosphere models for very low mass stars, brown dwarfs and exoplanets." Symposium - International Astronomical Union 189 (1997): 227–33. http://dx.doi.org/10.1017/s0074180900116729.

Повний текст джерела

Анотація:

Over the past decade considerable effort, both observational and theoretical, has been directed towards a more accurate determination of the stellar lower main sequence and of the sub-stellar domain covered by Brown Dwarfs and Planets. Astronomers have been looking for brown dwarfs for more than a decade, either with standard astronomical technics or with microlensing experiments. A breakthrough in the search for brown dwarfs was very recently achieved with the discovery of the first cool brown dwarf GL 229B (Nakajima et al. 1995). At the same epoch, the search for planets blossomed with the discovery of a Jupiter - mass companion of the star 51 Pegasi (Mayor and Queloz 199,5). Now, the number of faint, cool stars and substellar objects is rising rapidly.

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Day, Charles. "Young stars with brown dwarfs." Physics Today 68, no. 8 (August 2015): 23. http://dx.doi.org/10.1063/pt.3.2872.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

12

André, Philippe, Derek Ward-Thompson, and Jane Greaves. "Interferometric Identification of a Pre–Brown Dwarf." Science 337, no. 6090 (July 5, 2012): 69–72. http://dx.doi.org/10.1126/science.1222602.

Повний текст джерела

Анотація:

It is not known whether brown dwarfs [stellar-like objects with masses less than the hydrogen-burning limit, 0.075 solar mass (M☉)] are formed in the same way as solar-type stars or by some other process. Here we report the clear-cut identification of a self-gravitating condensation of gas and dust with a mass in the brown-dwarf regime, made through millimeter interferometric observations. The level of thermal millimeter continuum emission detected from this object indicates a mass ~0.02 to 0.03 M☉, whereas the small radius, <460 astronomical units, and narrow spectral lines imply a dynamical mass of 0.015 to 0.02 M☉. The identification of such a pre–brown dwarf core supports models according to which brown dwarfs are formed in the same manner as hydrogen-burning stars.

Стилі APA, Harvard, Vancouver, ISO та ін.

13

E. Potter, Daniel, Eduardo L. Martín, and Michael C. Cushing. "A Search for Brown Dwarfs around Young Solar-Analog Stars Using the Hōkūpa'a/Gemini Adaptive Optics System." Symposium - International Astronomical Union 211 (2003): 265–68. http://dx.doi.org/10.1017/s007418090021070x.

Повний текст джерела

Анотація:

We present the results of a search for low-mass companions around a sample of young, solar-analog stars using the Hōkūpa'a adaptive optics instrument mounted on the Gemini North 8 m telescope. Out of 31 stars observed, one binary brown dwarf system was found as a companion to the star HD 130948 (HIP 72567), as confirmed by proper motion and near-IR spectra. Orbital motion between the two brown dwarfs was measured, but our 14 month time baseline is inadequate to accurately measure the system's dynamical mass. Upcoming spectroscopic observations of the brown dwarfs will measure their lithium absorption lines to provide a more accurate age estimate of the system. The eventual dynamical mass determination coupled with the age determination will provide a valuable check of brown dwarf evolutionary models.

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Guenther, Eike, and Guenther Wuchterl. "Searching for Planets of Brown Dwarfs." Symposium - International Astronomical Union 211 (2003): 225–32. http://dx.doi.org/10.1017/s0074180900210632.

Повний текст джерела

Анотація:

Up to now, most planet search projects have concentrated on G and K stars. In order to considerably widen the view, we have stated a survey for planets of old, nearby brown dwarfs and very low-mass stars. Using UVES, we have observed 26 brown dwarfs and very low-mass stars. As it turned out these objects are very inactive and thus highly suitable for such a project. For 19 objects, we can exclude a planet with the mass of 3 MJ, and a period of 100 days or less with a probability of more than 60%. For these objects, we can also exclude Pegasi-planets with a high probability. For another 4 objects, we can exclude at least a brown dwarf companion. One object is a double line spectroscopic binary, and one object shows significant radial-velocity variations that can not be caused by a normal stellar-spot. This object either has a planetary-mass companion, or the variations are caused by surface structures that are quite different from normal star-spots.

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Zhang (张曾华), Z. H., A. J. Burgasser, M. C. Gálvez-Ortiz, N. Lodieu, M. R. Zapatero Osorio, D. J. Pinfield, and F. Allard. "Primeval very low-mass stars and brown dwarfs – VI. Population properties of metal-poor degenerate brown dwarfs." Monthly Notices of the Royal Astronomical Society 486, no. 1 (March 14, 2019): 1260–82. http://dx.doi.org/10.1093/mnras/stz777.

Повний текст джерела

Анотація:

ABSTRACT We presented 15 new T dwarfs that were selected from UKIRT Infrared Deep Sky Survey, Visible and Infrared Survey Telescope for Astronomy , and Wide-field Infrared Survey Explorer surveys, and confirmed with optical to near-infrared spectra obtained with the Very Large Telescope and the Gran Telescopio Canarias. One of these new T dwarfs is mildly metal-poor with slightly suppressed K-band flux. We presented a new X-shooter spectrum of a known benchmark sdT5.5 subdwarf, HIP 73786B. To better understand observational properties of brown dwarfs, we discussed transition zones (mass ranges) with low-rate hydrogen, lithium, and deuterium burning in brown dwarf population. The hydrogen burning transition zone is also the substellar transition zone that separates very low-mass stars, transitional, and degenerate brown dwarfs. Transitional brown dwarfs have been discussed in previous works of the Primeval series. Degenerate brown dwarfs without hydrogen fusion are the majority of brown dwarfs. Metal-poor degenerate brown dwarfs of the Galactic thick disc and halo have become T5+ subdwarfs. We selected 41 T5+ subdwarfs from the literature by their suppressed K-band flux. We studied the spectral-type–colour correlations, spectral-type–absolute magnitude correlations, colour–colour plots, and HR diagrams of T5+ subdwarfs, in comparison to these of L–T dwarfs and L subdwarfs. We discussed the T5+ subdwarf discovery capability of deep sky surveys in the 2020s.

Стилі APA, Harvard, Vancouver, ISO та ін.

16

F. Sterzik, Michael, and Richard H. Durisen. "Brown Dwarf Companion Frequencies and Dynamical Interactions." Symposium - International Astronomical Union 211 (2003): 35–38. http://dx.doi.org/10.1017/s007418090021022x.

Повний текст джерела

Анотація:

Numerical simulations are used to explore how gravitational interactions within young multiple star systems may determine the binary properties of brown dwarfs. We compare different scenarios for cluster formation and decay and find that brown dwarf binaries, although possible, generally have a low frequency. We also discuss the frequencies of brown dwarf companions to normal stars expected from these models.

Стилі APA, Harvard, Vancouver, ISO та ін.

17

Grieves, Nolan, François Bouchy, Monika Lendl, Theron Carmichael, Ismael Mireles, Avi Shporer, Kim K. McLeod, et al. "Populating the brown dwarf and stellar boundary: Five stars with transiting companions near the hydrogen-burning mass limit." Astronomy & Astrophysics 652 (August 2021): A127. http://dx.doi.org/10.1051/0004-6361/202141145.

Повний текст джерела

Анотація:

We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS objects of interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 MJup , and radii between 0.81 and 1.66 RJup . These targets have masses near the uncertain lower limit of hydrogen core fusion (~73-96 MJup ), which separates brown dwarfs and low-mass stars. We constrained young ages for TOI-587 (0.2 ± 0.1 Gyr) and TOI-681 (0.17 ± 0.03 Gyr) and found them to have relatively larger radii compared to other transiting companions of a similar mass. Conversely we estimated older ages for TOI-148 and TOI-746 and found them to have relatively smaller companion radii. With an effective temperature of 9800 ± 200 K, TOI-587 is the hottest known main-sequence star to host a transiting brown dwarf or very low-mass star. We found evidence of spin-orbit synchronization for TOI-148 and TOI-746 as well as tidal circularization for TOI-148. These companions add to the population of brown dwarfs and very low-mass stars with well measured parameters ideal to test formation models of these rare objects, the origin of the brown dwarf desert, and the distinction between brown dwarfs and hydrogen-burning main sequence stars.

Стилі APA, Harvard, Vancouver, ISO та ін.

18

C. Liu, Michael. "Disks around Young Brown Dwarfs." Symposium - International Astronomical Union 211 (2003): 133–36. http://dx.doi.org/10.1017/s0074180900210425.

Повний текст джерела

Анотація:

We present some results from a systematic survey for disks around spectroscopically identified young brown dwarfs and very low mass stars. We find that ≈75% of our sample show intrinsic IR excesses, indicative of circum(sub)stellar disks. The observed excesses are well-correlated with Hα emission, consistent with a common disk accretion origin. Because the excesses are modest, conventional analyses using only IR colors would have missed most of the sources with disks. In the same star-forming regions, we find that disks around brown dwarfs and T Tauri stars are contemporaneous; assuming coevality, this demonstrates that substellar disks are at least as long-lived as stellar disks. Altogether, the frequency and properties of circumstellar disks are similar from the stellar regime down to the substellar and planetary-mass regime. This offers compelling evidence of a common origin for most stars and brown dwarfs.

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Nguyen-Thanh, D., N. Phan-Bao, S. J. Murphy, and M. S. Bessell. "Sporadic and intense accretion in a 1 Myr-old brown dwarf candidate." Astronomy & Astrophysics 634 (February 2020): A128. http://dx.doi.org/10.1051/0004-6361/201936810.

Повний текст джерела

Анотація:

Context. Studying the accretion process in very low-mass objects has important implications for understanding their formation mechanism. Many nearby late-M dwarfs that have previously been identified in the field are in fact young brown dwarf members of nearby young associations. Some of them are still accreting. They are therefore excellent targets for further studies of the accretion process in the very low-mass regime at different stages. Aims. We aim to search for accreting young brown dwarf candidates in a sample of 85 nearby late-M dwarfs. Methods. Using photometric data from DENIS, 2MASS, and WISE, we constructed the spectral energy distribution of the late- M dwarfs based on BT-Settl models to detect infrared excesses. We then searched for lithium and Hα emission in candidates that exhibit infrared excesses to confirm their youth and the presence of accretion. Results. Among the 85 late-M dwarfs, only DENIS-P J1538317−103850 (M5.5) shows strong infrared excesses in WISE bands. The detection of lithium absorption in the M5.5 dwarf and its Gaia trigonometric parallax indicate an age of ~1 Myr and a mass of 47 MJ. The Hα emission line in the brown dwarf shows significant variability that indicates sporadic accretion. This 1 Myr-old brown dwarf also exhibits intense accretion bursts with accretion rates of up to 10−7.9 M⊙ yr−1. Conclusions. Our detection of sporadic accretion in one of the youngest brown dwarfs might imply that sporadic accretion at early stages could play an important role in the formation of brown dwarfs. Very low-mass cores would not be able to accrete enough material to become stars, and thus they end up as brown dwarfs.

Стилі APA, Harvard, Vancouver, ISO та ін.

20

J. Armitage, Philip, and Ian A. Bonnell. "Orbital Migration and the Brown Dwarf Desert." Symposium - International Astronomical Union 211 (2003): 31–34. http://dx.doi.org/10.1017/s0074180900210218.

Повний текст джерела

Анотація:

The orbital elements of extreme mass ratio binaries will be modified by interactions with surrounding circumstellar disks. For brown dwarf companions to Solar-type stars the resulting orbital migration is sufficient to drive short period systems to merger, creating a brown dwarf desert at small separations. We highlight the similarities and the differences between the migration of brown dwarfs and massive extrasolar planets, and discuss how observations can test a migration model for the brown dwarf desert.

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Luberto, Judah, Emily C. Martin, Peter McGill, Alexie Leauthaud, Andrew J. Skemer, and Jessica R. Lu. "A Search for Predicted Astrometric Microlensing Events by Nearby Brown Dwarfs*." Astronomical Journal 164, no. 6 (November 16, 2022): 253. http://dx.doi.org/10.3847/1538-3881/ac9a41.

Повний текст джерела

Анотація:

Abstract Gravitational microlensing has the potential to provide direct gravitational masses of single, free-floating brown dwarfs, independent of evolutionary and atmospheric models. The proper motions and parallaxes of nearby brown dwarfs can be used to predict close future alignments with distant background stars that cause a microlensing event. Targeted astrometric follow up of the predicted microlensing events permits the brown dwarf’s mass to be measured. Predicted microlensing events are typically found via searching for a peak threshold signal using an estimate of the lens mass. We develop a novel method that finds predicted events that instead will lead to a target lens-mass precision. The main advantage of our method is that it does not require a lens-mass estimate. We use this method to search for predicted astrometric microlensing events occurring between 2014 and 2032 using a catalog of 1225 low-mass star and brown-dwarf lenses in the Solar Neighborhood of spectral type M6 or later and a background source catalog from DECaLS Data Release 9. The background source catalog extends to g = 23.95, providing a more dense catalog compared to Gaia. Our search did not reveal any upcoming microlensing events. We estimate the rate of astrometric microlensing event for brown dwarfs in the Legacy Survey and find it to be low ∼10−5 yr−1. We recommend carrying out targeted searches for brown dwarfs in front of the Galactic Bulge and Plane to find astrometric microlensing events that will allow the masses of single, free-floating brown dwarfs to be measured.

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Jones, Hugh R. A., and Mike R. S. Hawkins. "A Deep Large area Search for Low Luminosity Stars." Highlights of Astronomy 11, no. 1 (1998): 435. http://dx.doi.org/10.1017/s1539299600021675.

Повний текст джерела

Анотація:

In a recent survey for faint red stars from a digital stack of Schmidt plates a number of candidate objects were identified. Parallax’s for three of these objects have been reported showing them to have luminosities which interpreted within the available evolutionary models indicate them to be good brown dwarf candidates. Here we examine spectra of these objects and others from the plate stack. Using standard spectral indices we find that for a given spectral type their spectra are more consistent with the Pleiades brown dwarfs (PPL 15, Teide 1 and Calar 3) than with standard late-type M dwarfs. Our interpretation is that this is due to their selection by RF IN colours which at values > 3 preferentially selects objects with relatively low gravities. For late-type M dwarfs and brown dwarfs low gravities are expected to be a reliable indication of youth. We also notice that the stack objects generally have strong FeH absorption for their spectral type. Current model atmospheres suggest that FeH strongly increases in strength toward lower metallicities and lower temperatures. We believe that this is not consistent with the available observational evidence from late-type M dwarfs. It is possible that solid Fe is forming inthe low temperature atmospheres relatively depleting FeH strengths toward lower temperatures. We find some evidence that for dwarfs at low temperatures dust formation is less prevalent in lower gravity objects suggesting that dwarfs at low temperatures stronger FeH may be an indication of youth. In addition to the spectral evidence the three stack objects whose parallax’s have been measured show small tangential velocities which is a further indication of youth.

Стилі APA, Harvard, Vancouver, ISO та ін.

23

Zuckerman, B. "Brown Dwarfs in Binary Systems." Highlights of Astronomy 8 (1989): 119–22. http://dx.doi.org/10.1017/s1539299600007577.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Burgasser, Adam J. "Brown dwarfs: Failed stars, super jupiters." Physics Today 61, no. 6 (June 2008): 70–71. http://dx.doi.org/10.1063/1.2947658.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Tinney, C. G. "Brown dwarfs: the stars that failed." Nature 397, no. 6714 (January 1999): 37–40. http://dx.doi.org/10.1038/16195.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Reipurth, Bo, and Cathie Clarke. "Brown Dwarfs as Ejected Stellar Embryos: Observational Perspectives." Symposium - International Astronomical Union 211 (2003): 13–22. http://dx.doi.org/10.1017/s0074180900210188.

Повний текст джерела

Анотація:

We discuss a scenario in which brown dwarfs are formed like stars, except that their full collapse phases are interrupted through dynamical interactions in small multiple systems, leading to the ejection of the lightest member. This disintegration is a stochastic process, often resulting in the expulsion of newborn low mass stars, but when it occurs early enough the ejected stellar embryo will be a substellar object. This process may be so common at early ages that a large fraction of the ubiquitous brown dwarfs could have formed in this manner. Detailed gas dynamical simulations are required in order to better understand the details of the decay of small newborn multiple systems. We discuss the observational consequences of the ejection hypothesis, noting especially the importance of binaries with brown dwarf components as an observational test. Finally, we note that brown dwarfs that have recently been ejected may be so disturbed, by infall from the collapsing core and also by heavy accretion from perturbed circumstellar disks, that traditional spectral and luminosity criteria may fail to identify their substellar nature.

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Carson, Joseph, Stephen Eikenberry, Bernhard Brandl, J. C. Wilson, and T. L. Hayward. "CHAOS: The Cornell High-Order Adaptive Optics Survey for Brown Dwarfs." Symposium - International Astronomical Union 211 (2003): 271–74. http://dx.doi.org/10.1017/s0074180900210723.

Повний текст джерела

Анотація:

The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% complete, uses the Palomar Hale Telescope's adaptive optics system to survey 80 bright stars out to 13 parsecs. Using the telescope's AO Science camera, brown dwarf companions 4–200 AU can be identified using coronagraphic imaging and spectroscopic modes. We will be using monte carlo simulations to create population models consistent with the CHAOS data set.Currently, we have observed 70 systems out of a target sample of 80. Five candidate companions await follow-up observations. As of now, no systems in the target sample have shown strong evidence of having brown dwarf companions. These early results support previous speculations of a “brown dwarf desert” at orbital separations out to 200 AU.While the target sources revealed no evidence of brown dwarf companions, accompanying observations of calibration stars provided evidence of an early methane dwarf candidate around the binary system HD150451AB. Forty seven parsecs from earth, the candidate indicated a projected orbital separation of 280 AU.

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Lowrance, Patrick J. "Companions to Young Stars." Symposium - International Astronomical Union 211 (2003): 295–98. http://dx.doi.org/10.1017/s0074180900210796.

Повний текст джерела

Анотація:

Brown dwarfs occupy the important region in the mass range between stars and planets. Their existence, ambiguous until only recently, and their properties give insight into stellar and planetary formation. We present statistical results of an infrared, coronagraphic survey of young, nearby stars that includes probable companions to three young G-type stars, G1 503.2 (G2V), HD 102982 (G3V), and G1 577 (G5V). The companion to G1 577 is a possible binary brown dwarf, according to evolutionary models. A dynamical determination of the components' masses will be achievable in the near future and will provide an excellent test of the predictive ability of the evolutionary models.

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Nielsen, Eric L., Michael C. Liu, Zahed Wahhaj, Beth A. Biller, and Thomas L. Hayward. "The Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets around Young B and A Stars." Proceedings of the International Astronomical Union 8, S299 (June 2013): 60–61. http://dx.doi.org/10.1017/s1743921313007874.

Повний текст джерела

Анотація:

AbstractWe have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (≈1.5–2.5 M⊙) conducted to date and includes the planet hosts β Pic and Fomalhaut. Despite detecting two new brown dwarfs, our observations did not detect new planets around our target stars, and we present upper limits on the fraction of high-mass stars that can host giant planets that are consistent with our null result.

Стилі APA, Harvard, Vancouver, ISO та ін.

30

R. Bate, Matthew, Ian A. Bonnell, and Volker Bromm. "The Formation Mechanism and Resulting Properties of Brown Dwarfs." Symposium - International Astronomical Union 211 (2003): 27–30. http://dx.doi.org/10.1017/s0074180900210206.

Повний текст джерела

Анотація:

We present results from the most complex hydrodynamical star formation calculation performed to date. It follows the collapse and fragmentation of a large-scale turbulent molecular cloud to form dozens of stars and brown dwarfs. It resolves all fragmentation down to the opacity limit, binary stars with separations as small as 1 AU, and circumstellar disks with radii down to ≈ 10 AU. In this proceedings, we examine the formation mechanism of the brown dwarfs and compare the initial mass function and the properties of the brown dwarfs with observations.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Apai, Dániel, Ilaria Pascucci, Jeroen Bouwman, Antonella Natta, Thomas Henning, and Cornelis P. Dullemond. "The Onset of Planet Formation in Brown Dwarf Disks." Science 310, no. 5749 (October 20, 2005): 834–36. http://dx.doi.org/10.1126/science.1118042.

Повний текст джерела

Анотація:

The onset of planet formation in protoplanetary disks is marked by the growth and crystallization of sub–micrometer-sized dust grains accompanied by dust settling toward the disk mid-plane. Here, we present infrared spectra of disks around brown dwarfs and brown dwarf candidates. We show that all three processes occur in such cool disks in a way similar or identical to that in disks around low- and intermediate-mass stars. These results indicate that the onset of planet formation extends to disks around brown dwarfs, suggesting that planet formation is a robust process occurring in most young circumstellar disks.

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Sahlmann, Johannes, Damien Ségransan, Didier Queloz, and Stéphane Udry. "A possible dividing line between massive planets and brown-dwarf companions." Proceedings of the International Astronomical Union 6, S276 (October 2010): 117–20. http://dx.doi.org/10.1017/s1743921311020047.

Повний текст джерела

Анотація:

AbstractBrown dwarfs are intermediate objects between planets and stars. The lower end of the brown-dwarf mass range overlaps with the one of massive planets and therefore the distinction between planets and brown-dwarf companions may require to trace the individual formation process. We present results on new potential brown-dwarf companions of Sun-like stars, which were discovered using CORALIE radial-velocity measurements. By combining the spectroscopic orbits and Hipparcos astrometric measurements, we have determined the orbit inclinations and therefore the companion masses for many of these systems. This has revealed a mass range between 25 and 45 Jupiter masses almost void of objects, suggesting a possible dividing line between massive planets and sub-stellar companions.

Стилі APA, Harvard, Vancouver, ISO та ін.

33

Kouwenhoven, M. B. N., Yun Li, D. Stamatellos, and S. P. Goodwin. "Circumstellar disk fragmentation and the origin of massive planetary companions, brown dwarfs, and very low-mass stars." Proceedings of the International Astronomical Union 14, S345 (August 2018): 239–40. http://dx.doi.org/10.1017/s174392131800827x.

Повний текст джерела

Анотація:

AbstractThe low-mass end of the initial mass function remains poorly understood. In this mass range, very low-mass stars, brown dwarfs, and massive planets are able to form through a variety of physical processes. Here, we study the long-term evolution of disk-fragmented systems around low-mass stars, for the epoch up to 10 Myr (the typical lifetime of an embedded cluster) and up to 10 Gyr (the age of the Milky Way). We carry out N-body simulations to study the decay of disk-fragmented systems and the resulting end products. Our simulations indicate rapid decay and frequent physical collisions during the first 10 Myr. We find that disk fragmentation provides a viable mechanism for explaining hierarchical triple systems, the brown dwarf desert, single and binary brown dwarfs, and very low-mass binary systems in the solar neighbourhood.

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Reid, I. N. "Low-Luminosity Stars: Past and Future." Highlights of Astronomy 11, no. 1 (1998): 433–34. http://dx.doi.org/10.1017/s1539299600021663.

Повний текст джерела

Анотація:

The expression “low luminosity stars” is a descriptive category which spans a wide range of objects, from the oldest stellar remnants in the Galaxy (Wood) through failed stars (Jones, Gould) to the enigmatic MACHOs, discernible not in themselves but only through their effects on others (Bennet). All of these have attracted considerable attention in recent years, and significant progress has been achieved in each case, even if our understanding has failed to keep up with observations. However, it is in the area of brown dwarfs where the most dramatic results have been obtained. The existence of such objects has been predicted theoretically for well over thirty years, but predictions can fail. Thus the discovery of G1229B (Nakajima et al, 1995), an unambiguous substellar-mass object, followed by the detection of lithium in Teide 1 and Calar 3 in the Pleiades (Rebolo et al, 1996) mark a turning point in studies of brown dwarfs. The issue now is not whether they exist, but what are their properties as a class. With that in mind, a number of obvious questions arise.First, what is the most effective method of finding brown dwarfs? Both brown dwarfs and VLM stars have effective temperatures below 2500K. Hence, many surveys concentrated on searching for objects which were very red at near-infrared wavelengths, and the blue JHK colours exhibited by Gl 229B cameas something of a surprise. This should not have been the case, of course, since Tsuji (1964) predicted the presence of methane in such cool atmospheres well before the term ’brown dwarf’ was invented. Current theory, as summarised in these sessions by Tsuji and Burrows, predicts that, as one moves to lower temperatures, grain formation initially drives (J-K) redward, before grains settle below τ ~ 1 and CH4 absorption sets in. Throughout, however, the optical-to-IR colours, straddling the peak in the emergent flux distribution, become progressively redder (Reid, 1994). Those colours therefore offer the most effective means of identifying both GD 165B-like and Gl 229B-like sources - an argument reinforced by the first results from the IJK DENIS survey (Delfosse et al, 1997).

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Manjavacas, E., N. Lodieu, V. J. S. Béjar, M. R. Zapatero-Osorio, S. Boudreault, and M. Bonnefoy. "Spectral library of age-benchmark low-mass stars and brown dwarfs." Monthly Notices of the Royal Astronomical Society 491, no. 4 (December 27, 2019): 5925–50. http://dx.doi.org/10.1093/mnras/stz3441.

Повний текст джерела

Анотація:

ABSTRACT In recent years, some extremely red brown dwarfs have been discovered. They were believed to have a low surface gravity, but many of their spectral characteristics are similar to those of high-surface-gravity brown dwarfs, showing that the spectral characteristics of young brown dwarfs are poorly understood. We aim to test surface-gravity indicators in late-M and early-L brown dwarf spectra using data obtained with the X-shooter spectrograph at the Very Large Telescope. We select a benchmark sample of brown dwarf members of Chamaeleon I (∼2 Myr), Upper Scorpius (5−10 Myr), the Pleiades (132 ± 27 Myr) and Praesepe (590−790 Myr) with well-constrained ages and similar metallicities. We provide a consistent spectral classification of the sample in the optical and in the near-infrared. We measure the equivalent widths of their alkali lines, finding that they have a moderate correlation with age, especially for objects with spectral types M8 and later. We use spectral indices defined in the literature to estimate surface gravity, finding that their gravity assignment is accurate for 75 per cent of our sample. We investigate the correlation between red colour and age, finding that after ∼10 Myr, the colour does not change significantly for our sample with spectral types M6.0–L3.0. In this case, the red colours might be associated with circumstellar discs, ring structures, extinction, or viewing angle. Finally, we calculate the bolometric luminosity, and J and K bolometric corrections for our sample. We find that six objects are overluminous compared with other members of the same association. These objects are flagged as binary candidates by the Gaia survey.

Стилі APA, Harvard, Vancouver, ISO та ін.

36

Borgniet, S., A. M. Lagrange, N. Meunier, F. Galland, L. Arnold, N. Astudillo-Defru, J. L. Beuzit, et al. "Extrasolar planets and brown dwarfs around AF-type stars." Astronomy & Astrophysics 621 (January 2019): A87. http://dx.doi.org/10.1051/0004-6361/201833431.

Повний текст джерела

Анотація:

Context. The impact of stellar mass on the properties of giant planets is still not fully understood. Main-sequence (MS) stars more massive than the Sun remain relatively unexplored in radial velocity (RV) surveys, due to their characteristics which hinder classical RV measurements. Aims. Our aim is to characterize the close (up to ~2 au) giant planet (GP) and brown dwarf (BD) population around AF MS stars and compare this population to stars with different masses. Methods. We used the SOPHIE spectrograph located on the 1.93 m telescope at Observatoire de Haute-Provence to observe 125 northern, MS AF dwarfs. We used our dedicated SAFIR software to compute the RV and other spectroscopic observables. We characterized the detected substellar companions and computed the GP and BD occurrence rates combining the present SOPHIE survey and a similar HARPS survey. Results. We present new data on two known planetary systems around the F5-6V dwarfs HD 16232 and HD 113337. For the latter, we report an additional RV variation that might be induced by a second GP on a wider orbit. We also report the detection of 15 binaries or massive substellar companions with high-amplitude RV variations or long-term RV trends. Based on 225 targets observed with SOPHIE and/or HARPS, we constrain the BD frequency within 2–3 au around AF stars to be below 4% (1σ). For Jupiter-mass GPs within 2–3 au (periods ≤103 days), we find the occurrence rate to be 3.7−1+3% around AF stars with masses <1.5 M⊙, and to be ≤6% (1σ) around AF stars with masses >1.5 M⊙. For periods shorter than 10 days, we find the GP occurrence rate to be below 3 and 4.5% (1σ), respectively. Our results are compatible with the GP frequency reported around FGK dwarfs and are compatible with a possible increase in GP orbital periods with stellar mass as predicted by formation models.

Стилі APA, Harvard, Vancouver, ISO та ін.

37

Lew, Ben W. P., Dániel Apai, Yifan Zhou, Mark Marley, L. C. Mayorga, Xianyu Tan, Vivien Parmentier, Sarah Casewell, and Siyi Xu (许偲艺). "Mapping the Pressure-dependent Day–Night Temperature Contrast of a Strongly Irradiated Atmosphere with HST Spectroscopic Phase Curve." Astronomical Journal 163, no. 1 (December 13, 2021): 8. http://dx.doi.org/10.3847/1538-3881/ac3001.

Повний текст джерела

Анотація:

Abstract Many brown dwarfs are on ultrashort-period and tidally locked orbits around white dwarf hosts. Because of these small orbital separations, the brown dwarfs are irradiated at levels similar to hot Jupiters. Yet, they are easier to observe than hot Jupiters because white dwarfs are fainter than main-sequence stars at near-infrared wavelengths. Irradiated brown dwarfs are, therefore, ideal hot Jupiter analogs for studying the atmospheric response under strong irradiation and fast rotation. We present the 1.1–1.67 μm spectroscopic phase curve of the irradiated brown dwarf (SDSS1411-B) in the SDSS J141126.20 + 200911.1 brown dwarf–white dwarf binary with the near-infrared G141 grism of the Hubble Space Telescope Wide Field Camera 3. SDSS1411-B is a 50M Jup brown dwarf with an irradiation temperature of 1300 K and has an orbital period of 2.02864 hr. Our best-fit model suggests a phase-curve amplitude of 1.4% and places an upper limit of 11° for the phase offset from the secondary eclipse. After fitting the white dwarf spectrum, we extract the phase-resolved brown dwarf emission spectra. We report a highly wavelength-dependent day–night spectral variation, with a water-band flux variation of about 360% ± 70% and a comparatively small J-band flux variation of 37% ± 2%. By combining the atmospheric modeling results and the day–night brightness temperature variations, we derive a pressure-dependent temperature contrast. We discuss the difference in the spectral features of SDSS1411-B and hot Jupiter WASP-43b, as well as the lower-than-predicted day–night temperature contrast of J4111-BD. Our study provides the high-precision observational constraints on the atmospheric structures of an irradiated brown dwarf at different orbital phases.

Стилі APA, Harvard, Vancouver, ISO та ін.

38

McCarthy, Chris, B. Zuckerman, and E. E. Becklin. "There is a Brown Dwarf Desert of Companions Orbiting Stars between 75 and 1000 AU." Symposium - International Astronomical Union 211 (2003): 279–80. http://dx.doi.org/10.1017/s0074180900210747.

Повний текст джерела

Анотація:

We present results of the first large (> 100 stars) infrared coronographic search for substellar companions to nearby stars. The search consisted of two surveys of stars chosen for their youth and proximity to Earth: 1.) a 178 star infrared survey at Steward and Lick Observatories, with optical followup from Keck Observatory, capable of detecting companions with masses greater than 30MJ, orbiting between about 75 and 300 AU, 2.) a 102 star survey using the Keck telescope, capable of detecting extrasolar brown dwarfs and planets typically more massive than 10 MJ, orbiting between about 75 and 300 AU.This research resulted in the discovery of one brown dwarf companion, zero planets and 23 double stars. The frequency of brown dwarf companions (of any mass) to G, K and M stars orbiting between 75 and 300 AU is measured to be 1 ± 1 %. The frequency of massive (> 30 MJ) brown dwarf companions is found to be 0.6 ± 0.6 %. The frequency of giant planets with masses larger than 10 MJ, between 75 and 300 AU, is measured here for the first time to be no more than about 3 %.

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Chabrier, Gilles, and Romain Lenoble. "Probing the Milky Way Stellar and Brown Dwarf Initial Mass Function with Modern Microlensing Observations." Astrophysical Journal Letters 944, no. 2 (February 1, 2023): L33. http://dx.doi.org/10.3847/2041-8213/acadd3.

Повний текст джерела

Анотація:

Abstract We use recent microlensing observations toward the central bulge of the Galaxy to probe the overall stellar plus brown dwarf initial mass function (IMF) in these regions well within the brown dwarf domain. We find that the IMF is consistent with the same Chabrier IMF characteristic of the Galactic disk. In contrast, other IMFs suggested in the literature overpredict the number of short-time events, and thus of very low mass stars and brown dwarfs, compared with observations. This again supports the suggestion that brown dwarfs and stars predominantly form via the same mechanism. We show that claims for different IMFs in the stellar and substellar domains arise from an incorrect parameterization of the IMF. Furthermore, we show that the IMF in the central regions of the bulge seems to be bottom-heavy, as illustrated by the large number of short-time events compared with the other regions. This recalls our previous analysis of the IMF in massive early-type galaxies and suggests the same kind of two-phase formation scenario, with the central bulge initially formed under more violent, burst-like conditions than the rest of the Galaxy.

Стилі APA, Harvard, Vancouver, ISO та ін.

40

Schaffenroth, V., S. Geier, U. Heber, R. Gerber, D. Schneider, E. Ziegerer, and O. Cordes. "The MUCHFUSS photometric campaign." Astronomy & Astrophysics 614 (June 2018): A77. http://dx.doi.org/10.1051/0004-6361/201629789.

Повний текст джерела

Анотація:

Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which have lost almost all of their hydrogen envelope. This mass loss is often triggered by common envelope interactions with close stellar or even substellar companions. Cool companions like late-type stars or brown dwarfs are detectable via characteristic light-curve variations like reflection effects and often also eclipses. To search for such objects, we obtained multi-band light curves of 26 close sdO/B binary candidates from the MUCHFUSS project with the BUSCA instrument. We discovered a new eclipsing reflection effect system (P = 0.168938 d) with a low-mass M dwarf companion (0.116 M⊙). Three more reflection effect binaries found in the course of the campaign have already been published; two of them are eclipsing systems, and in one system only showing the reflection effect but no eclipses, the sdB primary is found to be pulsating. Amongst the targets without reflection effect a new long-period sdB pulsator was discovered and irregular light variations were found in two sdO stars. The found light variations allowed us to constrain the fraction of reflection effect binaries and the substellar companion fraction around sdB stars. The minimum fraction of reflection effect systems amongst the close sdB binaries might be greater than 15% and the fraction of close substellar companions in sdB binaries may be as high as 8.0%. This would result in a close substellar companion fraction to sdB stars of about 3%. This fraction is much higher than the fraction of brown dwarfs around possible progenitor systems, which are solar-type stars with substellar companions around 1 AU, as well as close binary white dwarfs with brown dwarf companions. This might suggest that common envelope interactions with substellar objects are preferentially followed by a hot subdwarf phase.

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Jones, Hugh R. A. "Brown dwarfs: stars that never made it." Physics World 15, no. 11 (November 2002): 43–48. http://dx.doi.org/10.1088/2058-7058/15/11/43.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

42

Reid, I. N. "BROWN DWARFS: Failed Stars or Overachieving Planets?" Science 296, no. 5576 (June 21, 2002): 2154–55. http://dx.doi.org/10.1126/science.1074261.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

43

Whelan, E. T. "Jets from young stars and brown dwarfs." Astronomische Nachrichten 335, no. 5 (June 2014): 537–42. http://dx.doi.org/10.1002/asna.201412062.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

44

Jayawardhana, Ray. "Between Cool Stars and Hot Planets: Origins of Brown Dwarfs." Symposium - International Astronomical Union 219 (2004): 296–300. http://dx.doi.org/10.1017/s0074180900182269.

Повний текст джерела

Анотація:

Brown dwarfs, which straddle the mass range between stars and planets, appear to be common both in the solar neighborhood and in star-forming regions. Their ubiquity makes the question of their origin an important one both for our understanding of brown dwarfs themselves as well as for theories on the formation of stars and planets. Studies of young sub-stellar objects could provide valuable insight into their formation and early evolution. Here I report on the latest results from our observational programs at Keck, VLT and Magellan on the disk and accretion properties of young brown dwarfs. We find compelling evidence that they undergo a T Tauri phase analogous to that of their stellar counterparts.

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Jiang, Ing-Guey, G. Laughlin, and D. N. C. Lin. "On The Formation of Brown Dwarfs." International Astronomical Union Colloquium 191 (August 2004): 227–31. http://dx.doi.org/10.1017/s0252921100008812.

Повний текст джерела

Анотація:

AbstractThe observational properties of brown dwarfs pose challenges to the theory of star formation. Because their masses are much smaller than the typical Jeans mass of interstellar clouds, brown dwarfs are most likely formed through secondary fragmentation processes, rather than through the direct collapse of a molecular cloud core. In order to prevent substantial post-formation mass accretion, young brown dwarfs must leave the high-density formation regions in which they form. We propose here that brown dwarfs are formed in the optically thin outer regions of circumbinary disks. Through post-formation dynamical interaction with their host binary stars, young brown dwarfs are either scattered to large distance or removed, with modest speed, from their cradles.

Стилі APA, Harvard, Vancouver, ISO та ін.

46

Dupuy, Trent J., Michael C. Liu, and Michael J. Ireland. "Confronting substellar theoretical models with stellar ages." Proceedings of the International Astronomical Union 4, S258 (October 2008): 337–44. http://dx.doi.org/10.1017/s1743921309031998.

Повний текст джерела

Анотація:

AbstractBy definition, brown dwarfs never reach the main-sequence, cooling and dimming over their entire lifetime, thus making substellar models challenging to test because of the strong dependence on age. Currently, most brown dwarfs with independently determined ages are companions to nearby stars, so stellar ages are at the heart of the effort to test substellar models. However, these models are onlyfullyconstrained if both the mass and age are known. We have used the Keck adaptive optics system to monitor the orbit of HD 130948BC, a brown dwarf binary that is a companion to the young solar analog HD 130948A. The total dynamical mass of 0.109 ± 0.003 M⊙is the most precise mass measurement (3%) for any brown dwarf binary to date and shows that both components are substellar for any plausible mass ratio. The ensemble of available age indicators from the primary star suggests an age comparable to the Hyades, with the most precise age being 0.79+0.22−0.15Gyr based on gyrochronology. Therefore, HD 130948BC is unique among field L and T dwarfs as it possesses a well-determined mass, luminosity, and age. Our results indicate that substellar evolutionary models may underpredict the luminosity of brown dwarfs by as much as a factor of ≈2–3×. The implications of such a systematic error in evolutionary models would be far-reaching, for example, affecting determinations of the initial mass function and predictions of the radii of extrasolar gas-giant planets. This result is largely based on the reliability of stellar age estimates, and the case study of HD 130948A highlights the difficulties in determining the age of an arbitrary field star, even with the most up-to-date chromospheric activity and gyrochronology relations. In order to better assess the potential systematic errors present in substellar models, more refined age estimates for HD 130948A and other stars with binary brown dwarf companions (e.g., ϵ Ind Bab) are critically needed.

Стилі APA, Harvard, Vancouver, ISO та ін.

47

Rebolo, Rafael, Eduardo L. Martin, and Antonio Magazzu. "A Search for Lithium in Brown Dwarf Candidates." International Astronomical Union Colloquium 137 (1993): 171–73. http://dx.doi.org/10.1017/s0252921100017693.

Повний текст джерела

Анотація:

AbstractWe are conducting a search for lithium in very low mass objects with the aim of discriminating between stellar and substellar objects. Lithium is expected to be preserved in brown dwarfs with M/M⊙ ≤0.06, while it is known to be efficiently destroyed in low mass stars. In this paper we present high resolution observations in the region of the λ 6708 Li I resonance line of 5 very low mass dwarfs. In none of them lithium is detected, implying a Li destruction in their atmospheres of about four orders of magnitude. Our results suggest that these objects are probably very low mass stars rather than brown dwarfs.

Стилі APA, Harvard, Vancouver, ISO та ін.

48

Zhang (张曾华), Z. H., D. J. Pinfield, M. C. Gálvez-Ortiz, D. Homeier, A. J. Burgasser, N. Lodieu, E. L. Martín, et al. "Primeval very low-mass stars and brown dwarfs – III. The halo transitional brown dwarfs." Monthly Notices of the Royal Astronomical Society 479, no. 1 (May 23, 2018): 1383–91. http://dx.doi.org/10.1093/mnras/sty1352.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

49

Saffer, Rex A., and James Liebert. "The Search for Close Binary Evolved Stars." International Astronomical Union Colloquium 114 (1989): 408–12. http://dx.doi.org/10.1017/s0252921100099978.

Повний текст джерела

Анотація:

AbstractWe report on a search for short-period binary systems composed of pairs of evolved stars. The search is being carried out concurrently with a program to characterize the kinematical properties of two different samples of stars. Each sample has produced one close binary candidate for which further spectroscopic observations are planned. We also recapitulate the discovery of a close detached binary system composed of two cool DA white dwarfs, and we discuss the null results of Hα observations of the suspected white dwarf/brown dwarf system G 29–38.

Стилі APA, Harvard, Vancouver, ISO та ін.

50

Gagné, Jonathan, David Lafrenière, René Doyon, Jacqueline K. Faherty, Lison Malo, Kelle L. Cruz, Étienne Artigau, et al. "The BANYAN All-Sky Survey for Brown Dwarf Members of Young Moving Groups." Proceedings of the International Astronomical Union 10, S314 (November 2015): 49–53. http://dx.doi.org/10.1017/s1743921315006134.

Повний текст джерела

Анотація:

AbstractWe describe in this work the BASS survey for brown dwarfs in young moving groups of the solar neighborhood, and summarize the results that it generated. These include the discovery of the 2MASS J01033563–5515561 (AB)b and 2MASS J02192210–3925225 B young companions near the deuterium-burning limit as well as 44 new low-mass stars and 69 new brown dwarfs with a spectroscopically confirmed low gravity. Among those, ~20 have estimated masses within the planetary regime, one is a new L4 γ bona fide member of AB Doradus, three are TW Hydrae candidates with later spectral types (L1–L4) than all of its previously known members and six are among the first contenders for low-gravity ≥ L5 β/γ brown dwarfs, reminiscent of WISEP J004701.06+680352.1, PSO J318.5338–22.8603 and VHS J125601.92–125723.9 b. Finally, we describe a future version of this survey, BASS-Ultracool, that will specifically target ≥ L5 candidate members of young moving groups. First experimentations in designing the survey have already led to the discovery of a new T dwarf bona fide member of AB Doradus, as well as the serendipitous discoveries of an L9 subdwarf and an L5 + T5 brown dwarf binary.

Стилі APA, Harvard, Vancouver, ISO та ін.

Ми пропонуємо знижки на всі преміум-плани для авторів, чиї праці увійшли до тематичних добірок літератури. Зв'яжіться з нами, щоб отримати унікальний промокод!