Nikolaj Stevnbak Andersen
A5073963313- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Geological and Geochemical Analysis
- SAS software applications and methods
- Geomagnetism and Paleomagnetism Studies
- Astronomical Observations and Instrumentation
- Isotope Analysis in Ecology
- Galaxies: Formation, Evolution, Phenomena
- Metallurgical Processes and Thermodynamics
- High-pressure geophysics and materials
- Astrophysical Phenomena and Observations
- Metallurgy and Cultural Artifacts
- Food Quality and Safety Studies
Kolding Hospital
2020-2024
We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. combine these with prior studies to build a list of 525 known dwarfs within 20 pc the Sun, 38 which are presented here first time. Using published photometry spectroscopy as well our own follow-up, we an array color-magnitude color-color diagrams further characterize census members, provide polynomial fits bulk trends. characterizations, assign each object $T_{\rm eff}$ value judge sample completeness over bins...
Abstract A complete accounting of nearby objects—from the highest-mass white dwarf progenitors down to low-mass brown dwarfs—is now possible, thanks an almost set trigonometric parallax determinations from Gaia, ground-based surveys, and Spitzer follow-up. We create a census objects within Sun-centered sphere 20 pc radius check published literature decompose each binary or higher-order system into its separate components. The result is volume-limited ∼3600 individual star formation products...
Abstract We report the results of a spectroscopic survey candidate T subdwarfs identified by Backyard Worlds: Planet 9 program. Near-infrared spectra 31 sources with red J − W2 colors and large -band reduced proper motions show varying signatures subsolar metallicity, including strong collision-induced H 2 absorption, obscured methane water features, weak K i absorption. These metallicity are supported spectral model fits 3D velocities, indicating thick disk halo population membership for...
Abstract We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in multiepoch Wide-field Infrared Survey Explorer (WISE) images to identify previously unrecognized substellar neighbors Sun. measure [3.6]–[4.5] color phototype our dwarf candidates, with an emphasis on pinpointing coldest and closest Y within sample. The combination WISE astrometry provides...
Abstract Schneider et al. presented the discovery of WISEA J041451.67−585456.7 and J181006.18−101000.5, which appear to be first examples extreme T-type subdwarfs (esdTs; metallicity ≤−1 dex, T eff ≲ 1400 K). Here, we present new discoveries follow-up three subdwarf candidates, with an eye toward expanding sample such objects very low extraordinarily high kinematics, properties that suggest membership in Galactic halo. Keck/NIRES near-infrared spectroscopy J155349.96+693355.2, a fast-moving...
Abstract While stars are often found in binary systems, brown dwarf binaries much rarer. Brown dwarf–brown pairs typically difficult to resolve because they have very small separations. Using dwarfs discovered with data from the Wide-field Infrared Survey Explorer (WISE) via Backyard Worlds: Planet 9 citizen science project, we inspected other, higher-resolution, sky surveys for overlooked cold companions. During this process, system CWISE J0146−0508AB, which find has a chance alignment...
Abstract We present the discovery of 13 new widely separated T dwarf companions to M primaries, identified using Wide-field Infrared Survey Explorer/NEOWISE data by CatWISE and Backyard Worlds: Planet 9 projects (hereafter BYW). This sample represents an ∼60% increase in number known + systems, allows us probe most extreme products binary/planetary system formation, a space made available CatWISE2020 catalog BYW effort. Highlights among are WISEP J075108.79-763449.6, previously T9 thought be...
We present the discovery of WISEA J083011.95+283716.0, first Y dwarf candidate identified through Backyard Worlds: Planet 9 citizen science project. this object as a red, fast-moving source with faint $W2$ detection in multi-epoch \textit{AllWISE} and unWISE images. have characterized Spitzer Space Telescope \textit{Hubble Telescope} follow-up imaging. With mid-infrared detections \textit{Spitzer}'s \emph{ch1} \emph{ch2} bands flux upper limits Hubble $F105W$ $F125W$ filters, we find that is...
Abstract We have used data from the UKIRT Hemisphere Survey to search for substellar members of Hyades cluster. Our recovered several known members, and two brown dwarfs that we suggest may be based on a new kinematic analysis. uncovered thirteen candidates, obtained near-infrared follow-up spectroscopy each with IRTF/SpeX. Six candidates spectral types between M7 L0 are ruled out as potential their photometric distances (≳100 pc). The remaining seven L5 T4, all five showing strong...
A complete accounting of nearby objects -- from the highest-mass white dwarf progenitors down to low-mass brown dwarfs is now possible, thanks an almost set trigonometric parallax determinations Gaia, ground-based surveys, and Spitzer follow-up. We create a census within Sun-centered sphere 20-pc radius check published literature decompose each binary or higher-order system into its separate components. The result volume-limited $\sim$3,600 individual star formation products useful in...
We present the discovery of 13 new widely separated T dwarf companions to M primaries, identified using WISE/NEOWISE data by CatWISE and Backyard Worlds: Planet 9 projects. This sample represents a $\sim$60% increase in number known M+T systems, allows us probe most extreme products binary/planetary system formation, space made available CatWISE2020 catalog effort. Highlights among are WISEP J075108.79-763449.6, previously T9 thought be old due its SED, which we now find is part...
We have used the UKIRT Hemisphere Survey (UHS) combined with UKIDSS Galactic Cluster (GCS), Plane (GPS), and CatWISE2020 catalog to search for new substellar members of nearest open cluster Sun, Hyades. Eight Hyades candidate were identified observed Gemini/GNIRS near-infrared spectrograph. All eight objects are confirmed as brown dwarfs spectral types ranging from L6 T5, two showing signs binarity and/or variability. A kinematic analysis demonstrates that all discoveries likely belong...
Abstract We have used the UKIRT Hemisphere Survey combined with UKIDSS Galactic Cluster Survey, Plane and CatWISE2020 catalog to search for new substellar members of nearest open cluster Sun, Hyades. Eight Hyades candidate were identified observed Gemini/GNIRS near-infrared spectrograph. All eight objects are confirmed as brown dwarfs spectral types ranging from L6 T5, two showing signs binarity and/or variability. A kinematic analysis demonstrates that all discoveries likely belong cluster,...
We present the discovery of 118 new ultracool dwarf candidates, discovered using a machine learning tool, named \texttt{SMDET}, applied to time series images from Wide-field Infrared Survey Explorer. gathered photometric and astrometric data estimate each candidate's spectral type, distance, tangential velocity. This sample has photometrically estimated class distribution 28 M dwarfs, 64 L 18 T dwarfs. also identify subdwarf candidate, two extreme candidate young Five objects did not have...
Abstract We present the discovery of 118 new ultracool dwarf candidates, discovered using a machine-learning tool, named SMDET , applied to time-series images from Wide-field Infrared Survey Explorer. gathered photometric and astrometric data estimate each candidate’s spectral type, distance, tangential velocity. This sample has photometrically estimated class distribution 28 M dwarfs, 64 L 18 T dwarfs. also identify T-subdwarf candidate, two extreme candidate young Five objects did not have...
We report the results of a spectroscopic survey candidate T subdwarfs identified by Backyard Worlds: Planet 9 program. Near-infrared spectra 31 sources with red $J-W2$ colors and large $J$-band reduced proper motions show varying signatures subsolar metallicity, including strong collision-induced H$_2$ absorption, obscured methane water features, weak K I absorption. These metallicity are supported spectral model fits 3D velocities, indicating thick disk halo population membership for...