8 research outputs found
New nearby white dwarfs from Gaia DR1 TGAS and UCAC5/URAT
Using an accurate Gaia TGAS 25pc sample, nearly complete for GK stars, and
selecting common proper motion (CPM) candidates from UCAC5, we search for new
white dwarf (WD) companions around nearby stars with relatively small proper
motions. For investigating known CPM systems in TGAS and for selecting CPM
candidates in TGAS+UCAC5, we took into account the expected effect of orbital
motion on the proper motion as well as the proper motion catalogue errors.
Colour-magnitude diagrams (CMDs) and were used to verify
CPM candidates from UCAC5. Assuming their common distance with a given TGAS
star, we searched for candidates that occupied similar regions in the CMDs as
the few known nearby WDs (4 in TGAS) and WD companions (3 in TGAS+UCAC5). CPM
candidates with colours and absolute magnitudes corresponding neither to the
main sequence nor to the WD sequence were considered as doubtful or subdwarf
candidates. With a minimum proper motion of 60mas/yr, we selected three WD
companion candidates, two of which are also confirmed by their significant
parallaxes measured in URAT data, whereas the third may also be a chance
alignment of a distant halo star with a nearby TGAS star (angular separation of
about 465arcsec). One additional nearby WD candidate was found from its URAT
parallax and photometry. With HD 166435 B orbiting a well-known G1 star
at ~24.6pc with a projected physical separation of ~700AU, we discovered one of
the hottest WDs, classified by us as DA2.00.2, in the solar neighbourhood.
We also found TYC 3980-1081-1 B, a strong cool WD companion candidate around a
recently identified new solar neighbour with a TGAS parallax corresponding to a
distance of ~8.3pc and our photometric classification as ~M2 dwarf. This raises
the question whether previous assumptions on the completeness of the WD sample
to a distance of 13pc were correct.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
ASPECT: A spectra clustering tool for exploration of large spectral surveys
We present the novel, semi-automated clustering tool ASPECT for analysing
voluminous archives of spectra. The heart of the program is a neural network in
form of Kohonen's self-organizing map. The resulting map is designed as an icon
map suitable for the inspection by eye. The visual analysis is supported by the
option to blend in individual object properties such as redshift, apparent
magnitude, or signal-to-noise ratio. In addition, the package provides several
tools for the selection of special spectral types, e.g. local difference maps
which reflect the deviations of all spectra from one given input spectrum (real
or artificial). ASPECT is able to produce a two-dimensional topological map of
a huge number of spectra. The software package enables the user to browse and
navigate through a huge data pool and helps him to gain an insight into
underlying relationships between the spectra and other physical properties and
to get the big picture of the entire data set. We demonstrate the capability of
ASPECT by clustering the entire data pool of 0.6 million spectra from the Data
Release 4 of the Sloan Digital Sky Survey (SDSS). To illustrate the results
regarding quality and completeness we track objects from existing catalogues of
quasars and carbon stars, respectively, and connect the SDSS spectra with
morphological information from the GalaxyZoo project.Comment: 15 pages, 14 figures; accepted for publication in Astronomy and
Astrophysic
Galaxien-Kollisionen und das kosmische Feuerwerk der Quasare
Lange Zeiten wurden Galaxien als autarke Welteninseln
angesehen. Heute wissen wir, dass wechselseitige
Beeinflussungen die großen kosmischen Systeme
maßgeblich prägen und spektakuläre Prozesse in deren
Zentren auslösen können
-supported re-discovery of a remarkable weak line quasar from a variability and proper motion survey
We demonstrate that VPMS J170850.95+433223.7 is a weak line quasar (WLQ) which is remarkable in several respects. It was already classified as a probable quasar two decades ago, but with considerable uncertainty. The non-significant proper motion and parallax from the Gaia Early Data Release 3 have solidified this assumption. Based on previously unpublished spectra, we show that VPMS J170850.95+433223.7 is a WLQ at z = 2.345 with immeasurably faint broad emission lines in the rest-frame ultraviolet. A preliminary estimate suggests that it hosts a supermassive black hole of ∼109 M⊙ accreting close to the Eddington limit, perhaps at the super-Eddington level. We identify two absorber systems with blueward velocity offsets of 0.05c and 0.1c, which could represent high-velocity outflows, which are perhaps related to the high accretion state of the quasar