scholarly journals A search for millimeter emission from the coldest and closest brown dwarf with ALMA

2020 ◽  
Vol 642 ◽  
pp. A96
Author(s):  
Dirk Petry ◽  
Valentin D. Ivanov
Keyword(s):  
Magnetic Field ◽  
Calibration Procedure ◽  
The Sun ◽  
Brown Dwarf ◽  
Astronomical Observations ◽  
Link Type ◽  
Upper Limit ◽  
Unique Object ◽  
Upper Limits ◽  
Low Mass

Context. WISE J085510.83−071442.5 (W0855) is a unique object: with Teff ≈ 250 K it is the coldest known brown dwarf (BD), located at only ≈2.2 pc form the Sun. It is extremely faint, which makes any astronomical observations difficult. However, at least one remotely similar ultra-low-mass object, the M9 dwarf TVLM 513-46546, has been shown to be a steady radio emitter at frequencies up to 95 GHz with superimposed active states where strong, pulsed emission is observed. Aims. Our goal is to determine the millimeter radio properties of W0855 with deep observations around 93 GHz (3.2 mm) in order to investigate whether radio astrometry of this object is feasible and to measure or set an upper limit on its magnetic field. Methods. We observed W0855 for 94 min at 85.1–100.9 GHz on 24 December 2019 using 44 of the Atacama Large millimeter Array (ALMA) 12 m antennas. We used the standard ALMA calibration procedure and created the final image for our analysis by accommodating the Quasar 3C 209, the brightest nearby object by far. Furthermore, we created a light curve with a 30 s time resolution to search for pulsed emission. Results. Our observations achieve a noise RMS of 7.3 μJy beam−1 for steady emission and of 88 μJy for 30 s pulses in the aggregated bandwidth (Stokes I). There is no evidence for steady or pulsed emission from the object at the time of the observation. We derive 3σ upper limits of 21.9 μJy on the steady emission and of 264 μJy on the pulsed emission of W0855 between 85 GHz and 101 GHz. Conclusions. Together with the recent non-detection of W0855 at 4–8 GHz, our constraints on the steady and pulsed emission from W0855 confirm that the object is neither radio-loud nor magnetospherically particularly active.

On the Amount of Dust in the Asteroid Belt

1971 ◽  
Vol 12 ◽  
pp. 389-393
Author(s):  
Fred L. Whipple
Keyword(s):  
Solar Radiation ◽  
Particle Density ◽  
Asteroid Belt ◽  
Space Vehicles ◽  
The Sun ◽  
Small Particles ◽  
Zodiacal Cloud ◽  
Upper Limit ◽  
Upper Limits

Calculations of upper limits to the quantity of small particles in the asteroid belt are based on (1) the brightness of the counterglow coupled with observations and theory for the zodiacal cloud near Earth's orbit and (2) the destruction and erosion of asteroidal particles as they spiral toward the Sun because of solar radiation via the Poynting-Robertson effect. These calculations place the likely upper limit on asteroidal space particle density at the order of 5 to 10 times and the hazard to space vehicles at 2 to 4 times those near Earth's orbit. No such evidence indicates, however, that the hazard from small particles is actually much greater in the asteroid belt.

Discovery of a Brown Dwarf Very Close to the Sun: A Methane-rich Brown Dwarf Companion to the Low-Mass Star SCR 1845-6357

2006 ◽  
Vol 641 (2) ◽  
pp. L141-L144 ◽  
Author(s):  
B. A. Biller ◽  
M. Kasper ◽  
L. M. Close ◽  
W. Brandner ◽  
S. Kellner
Keyword(s):  
Mass Star ◽  
The Sun ◽  
Brown Dwarf ◽  
Low Mass

The Polarization of Thermal 'Solar Noise' and a Determination of the Sun's General Magnetic Field

1950 ◽  
Vol 3 (2) ◽  
pp. 265 ◽  
Author(s):  
SF Smerd
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Observational Evidence ◽  
Degree Of Polarization ◽  
The Sun ◽  
Maximum Phase ◽  
General Magnetic Field ◽  
Upper Limit ◽  
Surface Field

The equation of transfer of radiation and the magneto-ionic theory are used to derive expressions for the degree of polarization of thermal " solar noise " due to a general magnetic field of the sun. In particular, the net polarization of 600 Mc/s. (50 cm.) radiation corresponding to the maximum phase of the eclipse of November 1, 1948, as seen from Melbourne, Victoria, is evaluated theoretically and compared with observational evidence. This leads to an upper limit of 11 gauss for the surface field- strength at the solar poles at the time of observation.

scholarly journals Determining the mass of the planetary candidate HD 114762 b using Gaia

2019 ◽  
Vol 632 ◽  
pp. L9 ◽  
Author(s):  
Flavien Kiefer
Keyword(s):  
Spectral Analysis ◽  
Preceding Paper ◽  
Brown Dwarfs ◽  
Excess Noise ◽  
The Sun ◽  
Minimum Mass ◽  
Brown Dwarf ◽  
Data Release ◽  
Low Mass ◽  
M Dwarf

The first planetary candidate discovered by Latham et al. (1989, Nature, 339, 38) with radial velocities around a solar-like star other than the Sun, HD 114762 b, was detected with a minimum mass of 11 MJ. The small v sin i ∼ 0 km s−1 that is otherwise measured by spectral analysis indicated that this companion of a late-F subgiant star better corresponds to a massive brown dwarf (BD) or even a low-mass M-dwarf seen nearly face-on. To our knowledge, the nature of HD 114762 b is still undetermined. The astrometric noise measured for this system in the first data release, DR1, of the Gaia mission allows us to derive new constraints on the astrometric motion of HD 114762 and on the mass of its companion. We use the method GASTON, introduced in a preceding paper, which can simulate Gaia data and determine the distribution of inclinations that are compatible with the astrometric excess noise. With an inclination of 6.26.2+1.9−1.3 degree, the mass of the companion is constrained to Mb = 108+31−26 MJ. HD 114762 b thus indeed belongs to the M-dwarf domain, down to brown dwarfs, with Mb >  13.5 MJ at the 3σ level, and is not a planet.

ON THE LEFT TO RIGHT HAND TRANSITION PROBABILITY OF NEUTRINOS IN THE SUN

1989 ◽  
Vol 04 (23) ◽  
pp. 2243-2250 ◽  
Author(s):  
JOÃO PULIDO
Keyword(s):  
Magnetic Field ◽  
Adiabatic Approximation ◽  
Solar Magnetic Field ◽  
Transition Probability ◽  
Solar Neutrinos ◽  
Convective Zone ◽  
The Sun ◽  
Upper Limit ◽  
Favorable Case ◽  
Solar Field

The transition probability of left to right solar neutrinos in the sun is calculated in the adiabatic approximation as a function of the neutrino magnetic moment μν and the solar magnetic field depth and strength. We concentrate in the parameter regions compatible with the experimental upper limit μν<1.52×10−10μB and capable of providing a maximum VL→VR conversion. It is found that in the most favorable case (large innermost solar field B~104 G, small convective zone ~105 km and μν at its upper limit), this conversion is about 43% and decreases rapidly with decreasing μν.

scholarly journals Orbiting a binary

2017 ◽  
Vol 608 ◽  
pp. A106 ◽  
Author(s):  
M. Bonavita ◽  
V. D’Orazi ◽  
D. Mesa ◽  
C. Fontanive ◽  
S. Desidera ◽  
...  
Keyword(s):  
Near Infrared ◽  
Speckle Pattern ◽  
Major Axis ◽  
Brown Dwarf ◽  
Semi Major Axis ◽  
Similar Frequency ◽  
Link Type ◽  
Medium Resolution ◽  
Low Mass ◽  
Imaging Mode

Aims. In this paper we present the results of the SPHERE observation of the HD 284149 system, aimed at a more detailed characterisation of both the primary and its brown dwarf companion. Methods. We observed HD 284149 in the near-infrared with SPHERE, using the imaging mode (IRDIS+IFS) and the long-slit spectroscopy mode (IRDIS-LSS). The data were reduced using the dedicated SPHERE pipeline, and algorithms such as PCA and TLOCI were applied to reduce the speckle pattern. Results. The IFS images revealed a previously unknown low-mass (~0.16 M⊙) stellar companion (HD 294149 B) at ~0.1′′, compatible with previously observed radial velocity differences, as well as proper motion differences between Gaia and Tycho-2 measurements. The known brown dwarf companion (HD 284149 b) is clearly visible in the IRDIS images. This allowed us to refine both its photometry and astrometry. The analysis of the medium resolution IRDIS long slit spectra also allowed a refinement of temperature and spectral type estimates. A full reassessment of the age and distance of the system was also performed, leading to more precise values of both mass and semi-major axis. Conclusions. As a result of this study, HD 284149 ABb therefore becomes the latest addition to the (short) list of brown dwarfs on wide circumbinary orbits, providing new evidence to support recent claims that object in such configuration occur with a similar frequency to wide companions to single stars.

scholarly journals The Sun's gravitational quadrupole moment inferred from the fine structure of the acoustic and gravity normal mode spectra of the Sun

1986 ◽  
Vol 114 ◽  
pp. 345-354
Author(s):  
H. A. Hill ◽  
G. R. Rabaey ◽  
R. D. Rosenwald
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Angular Velocity ◽  
Magnetic Fields ◽  
Velocity Distribution ◽  
Quadrupole Moment ◽  
The Sun ◽  
Upper Limits ◽  
Gravity Mode ◽  
Theories Of Gravitation

The fine structure of the acoustic and gravity mode multiplets of the Sun have been analyzed to infer the internal rotation of the Sun and upper limits of the internal magnetic field. Observed fine structure for 137 multiplets has been obtained (Hill 1984b, 1985a, 1985b) and the fine structure has been examined for dependence on the angular order, m, of the modes. The inferred angular velocity distribution, together with the estimated upper limits on the internal magnetic fields, yields a gravitational quadrupole moment, J2, of ≈7.7 × 10−6. This result is consistent with the result obtained by Hill, Bos and Goode (1982) and has important implications for planetary tests of theories of gravitation.

A proto-brown dwarf candidate in rho Ophiuchus

2021 ◽  
Vol 32 ◽  
Author(s):  
Phan Bao Ngoc
Keyword(s):  
Formation Process ◽  
Brown Dwarfs ◽  
Small Scale ◽  
The Sun ◽  
Formation Processes ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Star Forming ◽  
Low Mass ◽  
Rho Ophiuchus

Brown dwarfs with masses below 0.075 solar masses are thought to form like low-mass stars (e.g., the Sun).However, it is still unclear how the physical formation processes occurin brown dwarfs at the ealiest stages (i.e., proto-brown dwarfs) of their formation.Up to date, only a few proto-brown dwarfs have been detected.The detection of proto-brown dwarfs offers us excellent benchmarks to studythe formation process of brown dwarfs, and thus understand their formation mechanism.In this paper, we present our identification of a proto-brown dwarf candidate in the star-forming regionrho Ophiuchus.The candidate shows a small-scale bipolar molecular outlfow that is similar to the outflows observed inother young brown dwarfs. The detection of this candidateprovides us with additional important implications for the formation mechanism of brown dwarfs.

scholarly journals GTC/CanariCam Deep Mid-infrared Imaging Survey of Northern Stars within 5 pc

2021 ◽  
Vol 923 (1) ◽  
pp. 119
Author(s):  
Bartosz Gauza ◽  
Víctor J. S. Béjar ◽  
Rafael Rebolo ◽  
Carlos Álvarez ◽  
María Rosa Zapatero Osorio ◽  
...  
Keyword(s):  
Infrared Imaging ◽  
Occurrence Rate ◽  
Brown Dwarf ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Mid Infrared ◽  
Deep Imaging ◽  
Upper Limits ◽  
Low Mass ◽  
Main Component

Abstract In this work we present the results of a direct imaging survey for brown dwarf companions around the nearest stars at the mid-infrared 10 micron range (λ c = 8.7 μm, Δλ = 1.1 μm) using the CanariCam instrument on the 10.4 m Gran Telescopio Canarias (GTC). We imaged the 25 nearest stellar systems within 5 pc of the Sun at declinations δ > −25° (at least half have planets from radial-velocity studies), reaching a mean detection limit of 11.3 ± 0.2 mag (1.5 mJy) in the Si-2 8.7 μm band over a range of angular separations from 1″ to 10″. This would have allowed us to uncover substellar companions at projected orbital separations between ∼2 and 50 au, with effective temperatures down to 600 K and masses greater than 30 M Jup assuming an average age of 5 Gyr and masses down to the deuterium-burning mass limit for objects with ages <1 Gyr. From the nondetection of such companions, we determined upper limits on their occurrence rate at depths and orbital separations yet unexplored by deep imaging programs. For the M dwarfs, the main component of our sample, we found with a 90% confidence level that fewer than 20% of these low-mass stars have L- and T-type brown dwarf companions with m ≳ 30 M Jup and T eff ≳ 600 K at ∼3.5–35 au projected orbital separations.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust &amp; Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust &amp; Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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