Radio emission in a nearby ultracool dwarf binary: a multi-frequency study
Juan B. Climent, J. C. Guirado, M. R. Zapatero-Osorio, O. V. Zakhozhay, M. A. Pérez-Torres, R. Azulay, B. Gauza, R. Rebolo, V. J. S. Béjar, J. Martín-Pintado, C. Lefèvre
备注：
Accepted for publication in A&A. 13 pages, 6 figures
The substellar triple system VHS J125601.92$-$125723.9 is composed by an equal-mass M7.5 brown dwarf binary and a L7 low-mass substellar object. In this work, we aim to identify the origin of the radio emission occurring in the central binary of VHS 1256$-$1257 while discussing the expected mechanisms involved in the radio emission of ultracool dwarfs (UCDs). We observed this system with the Karl G. Jansky Very Large Array, the European very-long-baseline interferometry (VLBI) Network, the enhanced Multi Element Remotely Linked Interferometer Network, the NOrthern Extended Millimeter Array, and the Atacama Large Millimetre Array at frequencies ranging from 5 GHz up to 345 GHz in several epochs during 2017, 2018, and 2019. We have found radio emission at 6 GHz and 33 GHz coincident with the expected position of the central binary of VHS~1256$-$1257. The Stokes I density flux detected were 73 $\pm$ 4 $μ$Jy and 83 $\pm$ 13 $μ$Jy, respectively, with no detectable circular polarisation or pulses. No emission is detected at higher frequencies (230 GHz and 345 GHz) nor at 5 GHz with VLBI arrays. The emission appears to be stable over almost 3 years at 6 GHz. To explain the constraints obtained both from the detections and non-detections we considered multiple scenarios including thermal and non-thermal emission, and different contributions from each component of the binary. Our results can be well explained by non-thermal gyrosynchrotron emission originating at radiation belts with a low plasma density (n$_e$ = 300$-$700 cm$^{-3}$), a moderate magnetic field strength (B $\approx$ 140 G), and an energy distribution of electrons following a power-law ($d N / d E \propto E^{- δ}$) with $δ$ fixed at 1.36. These radiation belts would need to be present in both components and also be viewed equatorially.
We present the results of a study to discover prospective new white dwarf-L dwarf binaries as identified by their near-infrared excesses in the UKIDSS catalogue. We obtained optical spectra to validate the white dwarf nature for 22 of the candidate primary stars, confirming ten as white dwarfs and determining their effective temperatures and gravities. For all ten white dwarfs we determined that the near-infrared excess was indeed indicative of a cool companion. Six of these are suggestive of late M dwarf companions, and three are candidate L dwarf companions, with one straddling the M$-$L bou…
Estimating Photometric Distances to Ultracool Dwarfs in Next Generation Space-based Infrared Surveys: Synthetic Photometry and New Absolute Magnitude Versus Spectral Type Relations for JWST, Euclid, and Roman Filters
Ultracool dwarf stars and brown dwarfs provide a unique probe of large-scale Galactic structure and evolution; however, until recently spectroscopic samples of sufficient size, depth, and fidelity have been unavailable. Here, we present the identification of 164 M7--T9 ultracool dwarfs in 0.6~deg$^2$ of deep, low-resolution, near-infrared spectroscopic data obtained with the Hubble Space Telescope Wide Field Camera 3 instrument as part of the WFC3 Infrared Spectroscopic Parallel Survey and the 3D-HST survey. We describe the methodology by which we isolate ultracool dwarf candidates from over 2…
Well-characterized binary systems will provide valuable opportunities to study the conditions that are necessary for the onset of both auroral and non-auroral magnetospheric radio emission in the ultracool dwarf regime. We present new detections of non-auroral "quiescent" radio emission at 4-8 GHz of the three ultracool dwarf binary systems GJ 564 BC, LP 415-20, and 2MASS J21402931+1625183. We also tentatively detect a highly circularly polarized pulse at 4-6 GHz that may indicate aurorae from GJ 564 BC. Finally, we show that the brightest binary ultracool dwarf systems may be more luminous th…
High resolution spectroscopy of the lowest-mass stars and brown dwarfs reveals their origins, multiplicity, compositions and physical properties, with implications for the star formation and chemical evolution history of the Milky Way. We motivate the need for high-resolution, infrared spectroscopic surveys to reach these faint sources.
Ultracool dwarfs have emerged as key targets for searches of transiting exoplanets. Precise estimates of the host parameters (including mass, age, and radius) are fundamental to constrain the physical properties of orbiting exoplanets. We have extended our evolutionary code CLES (Code Liégeois d'Evolution Stellaire) to the ultracool dwarf regime. We include relevant equations of state for H, He, as well as C and O elements to cover the temperature-density regime of ultracool dwarf interiors. For various metallicities, we couple the interior models to two sets of model atmospheres as surface bo…
SPHEREx Ultracool Dwarf spectrophotometric Atlas (SUDA): Atmospheric and Fundamental Parameters of Ultracool Dwarfs
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台光学天文重点实验室）；School of Astronomy and Space Sciences, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究中心）
The occurrence of planets orbiting ultracool dwarfs is poorly constrained. We present results from a Guest Observer program on NASA's K2 spacecraft to search for transiting planets orbiting a sample of 827 ultracool dwarfs. Having found no transiting planets in our sample, we determined an upper limit on the occurrence of planets. We simulated planets orbiting our sample for a range of orbital periods and sizes. For the simulated planets that transit their host, we injected the transit light curve into the real K2 light curves, then attempted to recover the injected planets. For a given occurr…
Astrometric planet search around southern ultracool dwarfs: V. Discovery of the exoplanet candidate PALTA-1 b
European Space Agency（欧洲空间局）；Main Astronomical Observatory, National Academy of Sciences of the Ukraine（乌克兰国家科学院主天文台）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Université de Genève（日内瓦大学）
With the discovery of a planetary system around TRAPPIST-1, there has been a surge of interest in ultracool dwarfs as potential planet hosts. Planetary systems around ultracool dwarfs represent our best chance of characterising temperate rocky-planet atmospheres with JWST. However, TRAPPIST-1 remains the only known system of its kind, and the occurrence rate of planets around ultracool dwarfs is still poorly constrained. We seek to perform a complete transit search on the ultracool dwarfs observed by NASA's K2 mission to constrain the occurrence rate of planets around these stars. We filter an…
We identify and investigate known ultracool stars and brown dwarfs that are being observed or indirectly constrained by the Gaia mission. These objects will be the core of the Gaia ultracool dwarf sample composed of all dwarfs later than M7 that Gaia will provide direct or indirect information on. We match known L and T dwarfs to the Gaia first data release, the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer AllWISE survey and examine the Gaia and infrared colours, along with proper motions, to improve spectral typing, identify outliers and find mismatches. There are 321…
Magnetic activity of ultracool dwarfs in the LAMOST DR11
Yunnan Observatories, Chinese Academy of Sciences（云南天文台，中国科学院）；Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences（天文物理重点实验室，中国科学院）；International Centre of Supernovae, Yunnan Key Laboratory（超新星国际中心，云南重点实验室）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（天文与空间科学学院，中国科学院大学）
We present the discovery of 255 binary and six multiple system candidates with wide > 5" separation composed by ultracool dwarfs companions to stars, plus nine double ultracool dwarf systems. These systems were selected based on common distance criteria. About 90% of the total sample has proper motions available and 73% of the systems also satisfy a common proper motion criterion. The sample of ultracool candidates was taken from the Dark Energy Survey (DES) and the candidate stellar primaries are from Gaia DR2 and DES data. We compute chance alignment probabilities in order to assess the phys…
The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey
上下文由于最近和正在进行的大规模调查，在过去十年中发现了数百颗褐矮星。加拿大-法国棕矮星巡天（英语：Canada-France Brown Dwarf Survey）是一项利用加拿大-法国-夏威夷望远镜（英语：Canada-France-Hawaii Telescope）上的MegaCam照相机进行的宽视场冷棕矮星巡天。目标。我们的目标是找到超冷的棕矮星，并从一个大的和均匀的L和T矮星样本约束场棕矮星光度函数和质量函数。方法.我们在CFHT/MegaCam i'和z'图像中确定候选者，并在几个望远镜上用指向近红外（NIR）成像跟踪它们。在我们的调查进行到一半时，我们发现了~50个T矮星和~170个L或超冷M矮星，这些矮星是从1400个候选者中抽取的，具有典型的超冷矮星i' - z'颜色，在780平方度内发现。结果我们目前已经完成了对所有候选者的大部分调查的近红外跟踪，从中L矮星到最新的T矮星，已知具有超冷矮星的颜色。这使我们能够利用一个完整的和定义良好的102个超冷矮星的样本来研究场矮星的光度函数和空间密度。结论.我们发现L5到T0晚期矮星的密度为2.0 pm0.8 x 10-3个pc-3，T0.5到T5.5矮星的密度为1.4 pm0.3 x 10-3个pc-3，T6到T8矮星的密度为5.3 pm3.1 x 10-3个pc-3。我们发现，这些结果更符合一个平坦的亚恒星质量函数。在T…
We describe our second installment of the 4.75 GHz survey of ultracool dwarfs (UCDs) conducted with the Arecibo radio telescope, which has observed 27 such objects and resulted in the detection of sporadic flaring from the T6 dwarf, WISEPC J112254.73+255021.5. We also present follow up observations of the first radio-emitting T dwarf, 2MASS J10475385+2124234, a tentatively identified radio emitting L1 dwarf, 2MASS J1439284+192915, and the known radio-flaring source, 2MASS J13142039+132011 AB. Our new data indicate that 2MASS J1439284+192915 is not a radio flaring source. The overall detection …
Ultracool dwarfs represent a significant proportion of stars in the Milky Way,and deep samples of these sources have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy. Until recently, spectral samples have been limited to the local volume (d<100 pc). Here, we analyze a sample of 164 spectroscopically-characterized ultracool dwarfs identified by Aganze et al. (2022) in the Hubble Space Telescope WFC3 Infrared Spectroscopic Parallel (WISP) Survey and 3D-HST. We model the observed luminosity function using population simulations to place constraints …
In this work, we identify 734 ultracool dwarfs with a spectral type of M6 or later, including one L0. Of this sample, 625 were studied spectroscopically for the first time. All of these ultracool dwarfs are within 360~pc, with a \textit{Gaia} G magnitude brighter than ~19.2 mag. By studying the spectra and checking their stellar parameters (Teff, logg, and [FeH] derived with the LAMOST pipeline, we found their cool red nature and their metallicity to be consistent with the nature of Galactic thin-disk objects. Furthermore, 77 of them show lithium absorption lines at 6708A, further indicating t…
(Abridged) We present a large, uniform analysis of young (~10-150 Myr) ultracool dwarfs, based on new high-precision IR parallaxes for 68 objects. We find that low-gravity (VL-G) late-M and L dwarfs form a continuous sequence in IR color-magnitude diagrams, separate from field objects and current theoretical models. VL-G objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting the two populations have a different range of physical properties. In contrast, at the L/T transition, young, old, and peculiar objects all span a narrow range in near-IR abso…
Ultracool and Brown Dwarf Candidates Identified via CatWISE-2MASS-Gaia DR3
Mount Saint Vincent University（圣文森特山大学）；Universidad Andres Bello（安德烈斯贝略大学）；Vatican Observatory（梵蒂冈天文台）；Universidade Federal de Santa Catarina（圣卡塔琳娜联邦大学）；INAF - Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）
We are conducting a proper-motion survey for young brown dwarfs in the Taurus-Auriga molecular cloud based on the Pan-STARRS1 3$π$ Survey. Our search uses multi-band photometry and astrometry to select candidates, and is wider (370 deg$^{2}$) and deeper (down to $\approx$3 M$_{\rm Jup}$) than previous searches. We present here our search methods and spectroscopic follow-up of our high-priority candidates. Since extinction complicates spectral classification, we have developed a new approach using low-resolution ($R \approx 100$) near-infrared spectra to quantify reddening-free spectral types, …
An interesting question about ultracool dwarfs recently raised in the literature is whether their emission is purely internally driven or partially powered by external processes similar to planetary aurora known from the solar system. In this work we present Hubble Space Telescope observations of the energy fluxes of the M8.5 ultracool dwarf LSR J1835+3259 throughout the UV. The obtained spectra reveal that the object is generally UV-fainter compared to other earlier-type dwarfs. We detect the \ion{Mg}{2} doublet at 2800 \A and constrain an average flux throughout the Near-UV. In the Far-UV wi…
Ultracool dwarfs encompass a wide variety of compact stellar-like objects with spectra classified as late-M, L, T and Y. Most of them have been discovered using wide-field imaging surveys. The Virtual Observatory has proven to be of great utility to efficiently exploit these astronomical resources. We aim to validate a Virtual Observatory methodology designed to discover and characterize ultracool dwarfs in deep extragalactic surveys like ALHAMBRA and COSMOS. Three complementary searches based on parallaxes, proper motions and colours, respectively were carried out. A total of 897 candidate ul…
We present a volume-limited, spectroscopically-verified sample of M7$-$L5 ultracool dwarfs within 25\,pc. The sample contains 410 sources, of which $93\%$ have trigonometric distance measurements ($80\%$ from \textit{Gaia} DR2), and $81\%$ have low-resolution ($R\sim120$), near-infrared (NIR) spectroscopy. We also present an additional list of 60 sources which may be M7$-$L5 dwarfs within 25\,pc when distance or spectral type uncertainties are taken into account. The spectra provide NIR spectral and gravity classifications, and we use these to identify young sources, red and blue $J-K_S$ color…
We report the results of a volume-limited survey using the Australia Telescope Compact Array to search for transient and quiescent radio emission from 15 southern hemisphere ultracool dwarfs. We detect radio emission from 2MASSW J0004348-404405 increasing the number of radio loud ultracool dwarfs to 22. We also observe radio emission from 2MASS J10481463-3956062 and 2MASSI J0339352-352544, two sources with previous radio detections. The radio emission from the three detected sources shows no variability or flare emission. Modelling this quiescent emission we find that it is consistent with opt…
One of the most promising avenues for the detailed study of temperate Earth-sized exoplanets is the detection of such planets in transit in front of stars small and nearby enough to make possible their thorough atmospheric characterisation with next generation telescopes like the James Webb Space telescope (JWST) or Extremely Large Telescope (ELT). In this context, the TRAPPIST-1 planets form an unique benchmark system that has gathered the interest of a large scientific community. The SPECULOOS survey is an exoplanet transit survey, that targets a volume-limited (40 pc) sample of ultracool dw…
The 5 GHz Arecibo Search for Radio Flares from Ultracool Dwarfs
我们提出了一个4.75 GHz的调查结果33褐矮星和一个年轻的系外行星系统的耀斑无线电发射，进行了305米阿雷西博射电望远镜。该计划的目标是探测和表征比光谱类型L3.5更冷的物体的磁场，这是我们调查之前探测到的最冷的棕矮星。我们还试图探测HR 8799行星系统的耀斑无线电发射，理论工作表明，热，大质量的系外行星可能具有强大的磁场，能够产生GHz频率的无线电发射。我们已经探测到并确认了来自T6.5矮星2 MASS J10475385+2124234的射电耀斑。这一发现极大地扩展了褐矮星似乎至少是零星的无线电发射体的温度范围，从~1900 K（L3.5）下降到~900 K（T6.5）。它还表明，无线电探测作为一种独特的工具，研究亚恒星物体的磁场的实用性延伸到最冷的矮星，并可能延伸到热的大质量系外行星。我们还从L1矮星2 MASS J1439284+192915中发现了一个3.6 σ的耀斑。这一发现是暂时的，需要通过额外的监测观察加以确认。
We present new calculations of Rosseland and Planck gaseous mean opacities relevant to the atmospheres of giant planets and ultracool dwarfs. Such calculations are used in modeling the atmospheres, interiors, formation, and evolution of these objects. Our calculations are an expansion of those presented in Freedman et al. (2008) to include lower pressures, finer temperature resolution, and also the higher metallicities most relevant for giant planet atmospheres. Calculations span 1 microbar to 300 bar, and 75 K to 4000 K, in a nearly square grid. Opacities at metallicities from solar to 50 tim…
The Gaia data release 2 (DR2) contains $>$6000 objects with parallaxes $(Plx+3\times{e\_Plx})>50$mas placing them within 20pc from the Sun. Since the expected numbers extrapolating the well-known 10pc census are much lower, nearby Gaia stars need a quality assessment. The 20pc sample of white dwarfs (WDs) had already been verified and completed with Gaia DR2. We aimed to check and complete the 20pc sample of ultracool dwarfs (UCDs) with spectral types $\gtrsim$M7 and given Gaia DR2 parallaxes. Dividing the Gaia DR2 20pc sample into subsamples of various astrometric and photometric quality, we …
