Discovery of Blackbody Stars and the Accuracy of SDSS photometry

2018 ◽  
Vol 14 (A30) ◽  
pp. 480-484
Author(s):  
Masataka Fukugita
Keyword(s):  
Trace Amount ◽  
White Dwarfs ◽  
Zero Point ◽  
Blackbody Radiation ◽  
Stellar Objects ◽  
Helium Atmosphere ◽  
Line Features ◽  
Zero Points

AbstractWe discovered stars that show spectra very close to the blackbody radiation without any line features. We found 17 such stars out of 0.8 million stellar objects in the SDSS archive. The blackbody temperature is approximately 104K. We identify these stars as DB white dwarfs with the helium atmosphere, possibly with a trace amount of hydrogen, that yields nearly perfect blackbody spectrum, which is also confirmed with our later study. These stars can be used to test the accuracy of the AB zero point across different colour bands, in particular including the NIR pass bands. The zero points of SDSS photometry are verified to < 0.01 mag.

scholarly journals Nature of blackbody stars

2019 ◽  
Vol 623 ◽  
pp. A177 ◽  
Author(s):  
Aldo Serenelli ◽  
René D. Rohrmann ◽  
Masataka Fukugita
Keyword(s):  
Physical Properties ◽  
Trace Amount ◽  
Blackbody Radiation ◽  
Sloan Digital Sky Survey ◽  
Helium Atmosphere ◽  
Sky Survey ◽  
Pure Helium ◽  
Effective Temperatures ◽  
Selection Of ◽  
The Continuum

A selection of 17 stars in the Sloan Digital Sky Survey, previously identified as DC-class white dwarfs (WDs), has been reported to show spectra very close to blackbody radiation in the wavelength range from ultraviolet to infrared. Because of the absence of lines and other details in their spectra, the surface gravity of these objects has previously been poorly constrained, and their effective temperatures have been determined by fits to the continuum spectrum using pure helium atmosphere models. We computed model atmospheres with pure helium and H/He mixtures and used Gaia DR2 parallaxes that are available for 16 of the 17 selected stars to analyze their physical properties. We find that the atmospheres of the selected stars are very probably contaminated with a trace amount of hydrogen of −6 ≤ log(NH/NHe) ≤ −5.4. For the 16 stars with Gaia parallaxes, we calculate a mean stellar mass 0.606 ± 0.076 M⊙, which represents typical mass values and surface gravities (7.8 <  logg <  8.3) for WDs.

Green's Forms and Meromorphic Functions on Compact Analytic Varieties

1951 ◽  
Vol 3 ◽  
pp. 108-128 ◽  
Author(s):  
Kunihiko Kodaira
Keyword(s):  
Meromorphic Function ◽  
Meromorphic Functions ◽  
Zero Point ◽  
Positive Definite ◽  
Analytic Surface ◽  
Analytic Variety ◽  
Complex Dimension ◽  
Analytic Varieties ◽  
Complex Analytic Variety ◽  
Zero Points

Let be a compact complex analytic variety of the complex dimension n with a positive definite Kâhlerian metric [4] ; the local analytic coordinates on will be denoted by z = (z 1 z 2, … , zn). Now, suppose a meromorphic function f(z) defined on as given. Then the poles and zero-points of f(z) constitute an analytic surface in consisting of a finite number of irreducible closed analytic surfaces Γ1, Γ2, … , Γk, each of which is a polar or a zero-point variety of f(z).

scholarly journals Towards Ensemble Asteroseismology of the Pulsating DB White Dwarf Stars

2002 ◽  
Vol 185 ◽  
pp. 608-609
Author(s):  
G. Handler ◽  
M.A. Wood ◽  
A. Nitta ◽  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
The Other ◽  
Archival Data ◽  
Dwarf Stars ◽  
Helium Atmosphere ◽  
Individual Stars ◽  
White Dwarf Stars ◽  
Binary Evolution ◽  
Insight Into

The origin of the helium-atmosphere DB white dwarfs is still a matter of debate. In particular, the question is unresolved whether binary evolution produces a significant number of DBs. The pulsating DB white dwarfs (DBV stars) offer a complementary insight into this problem through asteroseismology; DBs descending from binaries will have different interior structures than DBs originating from single stars (Nitta & Winget, 1998).GD 358 is by far the best-observed pulsating DBV star, and the only one for which asteroseismology has been performed to date. This star’s structure has been shown to be inconsistent with an origin from binary evolution (Nitta & Winget, 1998), but most of the other DBVs are relatively poorly studied.We therefore analysed archival data on all DBVs and obtained new measurements of stars with very little data available (Table 1), firstly to identify suitable targets for asteroseismological investigations and secondly to examine the pulsation spectra of the DBVs as a group, following the works of Clemens (1994) and Kleinman (1995) on the pulsating DA white dwarfs. Our study also produced new seismological results on individual stars and promising targets for future Whole Earth Telescope (WET, Nather et al., 1990) runs.

scholarly journals On the Spectral Evolution of Helium-atmosphere White Dwarfs Showing Traces of Hydrogen

2018 ◽  
Vol 857 (1) ◽  
pp. 56 ◽  
Author(s):  
B. Rolland ◽  
P. Bergeron ◽  
G. Fontaine
Keyword(s):  
White Dwarfs ◽  
Spectral Evolution ◽  
Helium Atmosphere

scholarly journals An Isolated White Dwarf with a 70 s Spin Period

2021 ◽  
Vol 923 (1) ◽  
pp. L6
Author(s):  
Mukremin Kilic ◽  
Alekzander Kosakowski ◽  
Adam G. Moss ◽  
P. Bergeron ◽  
Annamarie A. Conly
Keyword(s):  
White Dwarf ◽  
High Speed ◽  
White Dwarfs ◽  
Tangential Velocity ◽  
Large Mass ◽  
Atmospheric Composition ◽  
Instability Strip ◽  
Detailed Model ◽  
Helium Atmosphere ◽  
Spin Period

Abstract We report the discovery of an isolated white dwarf with a spin period of 70 s. We obtained high-speed photometry of three ultramassive white dwarfs within 100 pc and discovered significant variability in one. SDSS J221141.80+113604.4 is a 1.27 M ⊙ (assuming a CO core) magnetic white dwarf that shows 2.9% brightness variations in the BG40 filter with a 70.32 ± 0.04 s period, becoming the fastest spinning isolated white dwarf currently known. A detailed model atmosphere analysis shows that it has a mixed hydrogen and helium atmosphere with a dipole field strength of B d = 15 MG. Given its large mass, fast rotation, strong magnetic field, unusual atmospheric composition, and relatively large tangential velocity for its cooling age, J2211+1136 displays all of the signatures of a double white dwarf merger remnant. Long-term monitoring of the spin evolution of J2211+1136 and other fast-spinning isolated white dwarfs opens a new discovery space for substellar and planetary mass companions around white dwarfs. In addition, the discovery of such fast rotators outside of the ZZ Ceti instability strip suggests that some should also exist within the strip. Hence, some of the monoperiodic variables found within the instability strip may be fast-spinning white dwarfs impersonating ZZ Ceti pulsators.

Feed-Forward Control of an Arbitrary Pressure Pulsation Generator and its Application to Testing an Orifice-Type Flow Meter

2014 ◽  
Author(s):  
Tomonori Kato ◽  
Tetsuma Hirakawa ◽  
Mitsuhiro Nakao ◽  
Takashi Oowaku ◽  
Hirohisa Sakuma ◽  
...  
Keyword(s):  
Pressure Pulsation ◽  
Zero Point ◽  
Flow Meter ◽  
Pressure Regulator ◽  
Flow Meters ◽  
Feed Forward ◽  
Servo Valve ◽  
Feed Forward Control ◽  
Type Flow ◽  
Zero Points

This paper presents a compact arbitrary pressure pulsation generator for assessing the characteristics of flow meters and sensors, particularly around their zero points. In this study, a compact arbitrary pressure pulsation generator was created using some pneumatic components, such as a high-precision quick-response pneumatic pressure regulator (HPR) and a spool-type servo-valve. The feed-forward compensation of the controller provided the desired pressure pulse to the tested flow meter by controlling the spool-type servo valve; 30 Hz was achieved. In order to validate the effectiveness of the developed generator, we evaluated the dynamic characteristics around the zero point of an orifice-type flow meter in the range from 1 Hz through 30 Hz.

scholarly journals The Blue Stellar Objects of the First Byurakan Survey

2002 ◽  
Vol 184 ◽  
pp. 101-102
Author(s):  
A.M. Mickaelian
Keyword(s):  
Surface Density ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Seyfert Galaxies ◽  
Byurakan Survey ◽  
Stellar Objects ◽  
First Byurakan Survey ◽  
Hot Subdwarfs

AbstractThe Second part of the FBS is devoted to the discovery and study of blue stellar objects. It was carried out in an area of 4009 deg2 and identified 1103 objects: hot subdwarfs and white dwarfs, cataclysmic variables, QSOs and Seyfert galaxies, etc. The discovery of new bright QSOs led to a re-evaluation of their surface density (0.012 deg−2). Several interesting cataclysmic variables have been discovered as well.

Distances of nearby Groups and Clusters, and the Local Value of the Hubble Ratio

1977 ◽  
Vol 37 ◽  
pp. 301-307
Author(s):  
G. de Vaucouleurs
Keyword(s):  
Globular Clusters ◽  
Zero Point ◽  
Rr Lyrae ◽  
Galactic Clusters ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Absolute Magnitudes ◽  
Extragalactic Distance Scale ◽  
Zero Points ◽  
Local Value

AbstractThe correct approach to build up the extragalactic distance scale is to use all available primary (novae, cepheids, RR Lyrae) and secondary indicators (brightest stars, globular clusters, largest HII rings) to calibrate without arbitrary extrapolation all reliable tertiary indicators (magnitudes and diameters of galaxies), precisely corrected for all known effects of type, luminosity class, orientation, internal and galactic extinction and redshift. Such data are now available for over 1000 galaxies in the Second Reference Catalogue.Revised distances to members of the Local Group from primary indicators and new estimates of distances to the nearest groups from primary and secondary indicators are used to calibrate the tertiary indicators via a new, composite luminosity index.The distances derived from globular clusters for 3 galaxy clusters dominated by ellipticals (Vir I, For I, Hya I) with mean corrected velocities 1000 ≤ Vo ≤ 3650 km s-1 give a mean Hubble ratio <H> = 88 (1 ± 0.15) km s-1 Mpc-1. This value rests entirely on the calibration of the globular clusters luminosity function in the Galaxy as a gaussian of dispersion σ = 1.1 mag. and mean <MB>(⊕) = -6.55, with <(B-V)o > = 0.75, based on the adopted RR Lyrae zero point <Mv> (RR) = + 0.86 ± 0.15.The distances derived from tertiary indicators to 19 field spirals and 28 nearby groups dominated by spirals with corrected velocities Vo < 1800 km s-1 give <H> = 82 (1 ± 0.15) km s-1 Mpc-1. This value rests on the relations between luminosity index and fully corrected absolute magnitudes or linear diameters of galaxies derived without extrapolation and calibrated in ~20 nearby galaxies by seven secondary indicators. The zero points were derived from the 3 primary indicators, including 15 galactic novae with <M15> = -5.5 ± 0.15, and 13 cepheids in 8 galactic clusters with <MB> (logPo = 0.8) = -2.92 ± 0.15 (for an adopted Hyades modulus of 3.16 ± 0.05).The low values of Ho≃50 to 55 can be explained by an accumulation of complex systematic errors arising from a multiplicity of sources. These errors, all but one acting in the same sense, have been identified and evaluated; a full report will appear elsewhere.

scholarly journals Asteroseismology of GD358 with complex core carbon and oxygen profiles

2015 ◽  
Vol 11 (A29B) ◽  
pp. 489-492
Author(s):  
Agnès Bischoff-Kim ◽  
Judith L. Provencal
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Complete Data ◽  
Time Dependent ◽  
Archival Data ◽  
Data Set ◽  
Helium Atmosphere ◽  
Complex Core ◽  
Pure Helium ◽  
Oxygen Profiles

AbstractGD 358 is the brightest (mv=13.7) and best studied helium atmosphere white dwarf pulsator. We present an analysis based on over 1000 hours of observations spanning 2007-2014 as well as archival data going back to 1982. From the complete data set, we identify a total of 27 independent frequencies and fit 14 of them as m=0 modes in our asteroseismic analysis. We add GD358 to a set of helium atmosphere white dwarfs fitted with similar models. With this consistent set, we can see a trend in the thickness of the pure helium layer that are quantitatively consistent with time-dependent diffusion calculations.

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