Spacecraft Navigation Using X-Ray Pulsars
... and with their faint emissions, radio-based systems would require large antennas (on the order of 25 m in diameter or larger) to detect sources, which would be impractical for most spacecraft. Also, neighboring celestial objects including the sun, moon, Jupiter, and close stars, as well as distance ...
... and with their faint emissions, radio-based systems would require large antennas (on the order of 25 m in diameter or larger) to detect sources, which would be impractical for most spacecraft. Also, neighboring celestial objects including the sun, moon, Jupiter, and close stars, as well as distance ...
Clusters: age scales for stellar physics
... and theory. Thus, observational phenomena with very well defined ages, our anchors, are extremely important. As a matter of fact, there is a scarcity of them and, moreover, several results do not agree with each other completely. One example is the different age scales for open clusters, since there ...
... and theory. Thus, observational phenomena with very well defined ages, our anchors, are extremely important. As a matter of fact, there is a scarcity of them and, moreover, several results do not agree with each other completely. One example is the different age scales for open clusters, since there ...
Characterizing the Cool KOIs III. KOI
... to Barnard’s Star, yet shares its effective temperature, consistent with the K-band measurements. In Section 3 we perform a more quantitative assessment of KOI-961’s stellar properties relative to Barnard’s Star. We start with empirical measurements of the mass, radius and luminosity of Barnard’s St ...
... to Barnard’s Star, yet shares its effective temperature, consistent with the K-band measurements. In Section 3 we perform a more quantitative assessment of KOI-961’s stellar properties relative to Barnard’s Star. We start with empirical measurements of the mass, radius and luminosity of Barnard’s St ...
Star Formation and Dynamics in the Galactic Centre
... (e.g. Sunyaev et al. 1993), especially the 6.4 keV Fe Kα line. This line is emitted by various molecular clouds in the GC (e.g. Ponti et al. 2010). The lines emitted from different clouds might be triggered by different sources (e.g. different X-ray binaries), but this possibility is not supported b ...
... (e.g. Sunyaev et al. 1993), especially the 6.4 keV Fe Kα line. This line is emitted by various molecular clouds in the GC (e.g. Ponti et al. 2010). The lines emitted from different clouds might be triggered by different sources (e.g. different X-ray binaries), but this possibility is not supported b ...
thesis
... In recent years the research field of single, low-mass star formation has seen an enormous development, both due to new ground-based and space-based instruments and observational techniques, and due to the development of astrophysical theories that support these observations. Star formation occurs i ...
... In recent years the research field of single, low-mass star formation has seen an enormous development, both due to new ground-based and space-based instruments and observational techniques, and due to the development of astrophysical theories that support these observations. Star formation occurs i ...
PDF only - at www.arxiv.org.
... higher sensitivity. Together with a larger collecting area compared to Herschel observations of dedicated solar longitudes over a full martian year would provide for the first time vertical H2O2 profiles and in a unique way constrain photochemical models. Other important species are ...
... higher sensitivity. Together with a larger collecting area compared to Herschel observations of dedicated solar longitudes over a full martian year would provide for the first time vertical H2O2 profiles and in a unique way constrain photochemical models. Other important species are ...
Ultra-luminous Quasars with the Most Massive Black Holes at
... The first low-resolution optical spectrum of this source was obtained with the Lijiang 2.4 m telescope using the YFOSC on 2013 November 25 (UT), then follow-up by Magellan. ...
... The first low-resolution optical spectrum of this source was obtained with the Lijiang 2.4 m telescope using the YFOSC on 2013 November 25 (UT), then follow-up by Magellan. ...
S282_2 Introduction to active galaxies
... Normal galaxies Normal galaxies are made up of stars and (in the case of spiral and irregular galaxies) gas and dust. Their spectra consist of the sum of the spectra of these components. The optical spectra of normal stars are continuous spectra overlaid by absorption lines (Figure 1). There are tw ...
... Normal galaxies Normal galaxies are made up of stars and (in the case of spiral and irregular galaxies) gas and dust. Their spectra consist of the sum of the spectra of these components. The optical spectra of normal stars are continuous spectra overlaid by absorption lines (Figure 1). There are tw ...
Stellar Wind Mechanisms and Instabilities
... temperature, this parameter is still quite small, s∗ ∼ 10−3 . As discussed further in §3, for the multi-million-degree temperature of the solar corona, this parameter is much closer to unity, and that is a key factor in the capacity for the thermal gas pressure to drive the outward coronal expansion ...
... temperature, this parameter is still quite small, s∗ ∼ 10−3 . As discussed further in §3, for the multi-million-degree temperature of the solar corona, this parameter is much closer to unity, and that is a key factor in the capacity for the thermal gas pressure to drive the outward coronal expansion ...
Turbulence-driven Polar Winds from T Tauri Stars Energized by
... The “cold wave-driven wind” limit • When the plasma becomes massive enough, radiative cooling (~ρ2) becomes more efficient throughout the wind: ...
... The “cold wave-driven wind” limit • When the plasma becomes massive enough, radiative cooling (~ρ2) becomes more efficient throughout the wind: ...
Photospheric activity, rotation, and star
... The polar flattening of the star due to the centrifugal potential is computed in the Roche approximation with a rotation period of 6.35 days. The relative difference between the equatorial and the polar radii is 1.71 × 10−4 which induces a completely negligible relative flux variation of ≈10−6 for ...
... The polar flattening of the star due to the centrifugal potential is computed in the Roche approximation with a rotation period of 6.35 days. The relative difference between the equatorial and the polar radii is 1.71 × 10−4 which induces a completely negligible relative flux variation of ≈10−6 for ...
The Formation and Early Evolution of Young Massive Clusters
... this case formation can proceed “in situ” – i.e. the stars form at protostellar densities close to the final stellar density. Conversely, in the disk, the gas either begins forming stars while it is being accumulated to high density, in a “conveyor belt” mode, or the time scale to accumulate the gas ...
... this case formation can proceed “in situ” – i.e. the stars form at protostellar densities close to the final stellar density. Conversely, in the disk, the gas either begins forming stars while it is being accumulated to high density, in a “conveyor belt” mode, or the time scale to accumulate the gas ...
Radio Emission Toward Regions of Massive Star Formation
... stars with accretion disks and bipolar outflows have been directly observed (Kraus et al. 2010). Therefore, there must be some other important physics simple models do not take into account. The review by Zinnecker & Yorke (2007) discusses three prevailing theories: monolithic collapse in cores with ...
... stars with accretion disks and bipolar outflows have been directly observed (Kraus et al. 2010). Therefore, there must be some other important physics simple models do not take into account. The review by Zinnecker & Yorke (2007) discusses three prevailing theories: monolithic collapse in cores with ...
Title The Correlation between Dispersion Measure and X
... and c is the speed of light. Most free electrons in our Galaxy are found in the hot phase of the ISM, including H ii regions ionized by UV radiation from hot O or B type stars and the shock-heated interior of supernova remnants (SNRs). These sources can contribute significant DM up to a few hundred ...
... and c is the speed of light. Most free electrons in our Galaxy are found in the hot phase of the ISM, including H ii regions ionized by UV radiation from hot O or B type stars and the shock-heated interior of supernova remnants (SNRs). These sources can contribute significant DM up to a few hundred ...
The similarity of the stellar mass fractions of galaxy groups and
... studies mentioned above inferred the total stellar mass by applying a simple stellar M/L ratio conversion. L12 argue that applying a single conversion factor to all galaxies will bias the estimate of fstar , since not all galaxies in groups and clusters are quiescent and furthermore the fraction of ...
... studies mentioned above inferred the total stellar mass by applying a simple stellar M/L ratio conversion. L12 argue that applying a single conversion factor to all galaxies will bias the estimate of fstar , since not all galaxies in groups and clusters are quiescent and furthermore the fraction of ...
Studies of molecular clouds at the Galactic centre Roland Karlsson DECLINATION (B1950)
... PAPER I: I contributed to the preparation of the proposal to NRAO, as well as the full procedure for preparing and performing the observations, together with Aage Sandqvist, John Whiteoak and Frank Gardner. The post-observational calibration of the data was made at the VLA together with Aage Sandqvi ...
... PAPER I: I contributed to the preparation of the proposal to NRAO, as well as the full procedure for preparing and performing the observations, together with Aage Sandqvist, John Whiteoak and Frank Gardner. The post-observational calibration of the data was made at the VLA together with Aage Sandqvi ...
discovery of four new massive and dense cold cores
... single-dish telescopes have shown that massive stars form in regions of molecular gas with distinctive physical parameters, which we refer to as massive dense cores.1 For example, from observations of the CS (5 ! 4) line emission toward massive star–forming regions associated with H2O masers, Plume ...
... single-dish telescopes have shown that massive stars form in regions of molecular gas with distinctive physical parameters, which we refer to as massive dense cores.1 For example, from observations of the CS (5 ! 4) line emission toward massive star–forming regions associated with H2O masers, Plume ...
Stars, Galaxies, and Beyond
... Ivezić for allowing me this opportunity to explore these many important topics in astrophysics. Sources: The materials in this summary derive from the lecture notes, the assigned textbook, and many Web and published scientific articles and other sources as noted. I do not consider Wikipedia to be a ...
... Ivezić for allowing me this opportunity to explore these many important topics in astrophysics. Sources: The materials in this summary derive from the lecture notes, the assigned textbook, and many Web and published scientific articles and other sources as noted. I do not consider Wikipedia to be a ...
the formation of giant molecular clouds
... who always saw things so clearly. The numerical work presented here would have been impossible without the help of Lars Hernquist and Neal Katz, who provided a version of the TREESPH code in which they have invested so much time and effort. It is either a credit to Lars and Neal or a reflection on m ...
... who always saw things so clearly. The numerical work presented here would have been impossible without the help of Lars Hernquist and Neal Katz, who provided a version of the TREESPH code in which they have invested so much time and effort. It is either a credit to Lars and Neal or a reflection on m ...
Cygnus X-1
Cygnus X-1 (abbreviated Cyg X-1) is a well-known galactic X-ray source, thought to be a black hole, in the constellation Cygnus. It was discovered in 1964 during a rocket flight and is one of the strongest X-ray sources seen from Earth, producing a peak X-ray flux density of 6977229999999999999♠2.3×10−23 Wm−2 Hz−1 (7003230000000000000♠2.3×103 Jansky). Cygnus X-1 was the first X-ray source widely accepted to be a black hole and it remains among the most studied astronomical objects in its class. The compact object is now estimated to have a mass about 14.8 times the mass of the Sun and has been shown to be too small to be any known kind of normal star, or other likely object besides a black hole. If so, the radius of its event horizon is about 7004440000000000000♠44 km.Cygnus X-1 belongs to a high-mass X-ray binary system about 7019574266339685654♠6070 ly from the Sun that includes a blue supergiant variable star designated HDE 226868 which it orbits at about 0.2 AU, or 20% of the distance from the Earth to the Sun. A stellar wind from the star provides material for an accretion disk around the X-ray source. Matter in the inner disk is heated to millions of degrees, generating the observed X-rays. A pair of jets, arranged perpendicular to the disk, are carrying part of the energy of the infalling material away into interstellar space.This system may belong to a stellar association called Cygnus OB3, which would mean that Cygnus X-1 is about five million years old and formed from a progenitor star that had more than 7001400000000000000♠40 solar masses. The majority of the star's mass was shed, most likely as a stellar wind. If this star had then exploded as a supernova, the resulting force would most likely have ejected the remnant from the system. Hence the star may have instead collapsed directly into a black hole.Cygnus X-1 was the subject of a friendly scientific wager between physicists Stephen Hawking and Kip Thorne in 1975, with Hawking betting that it was not a black hole. He conceded the bet in 1990 after observational data had strengthened the case that there was indeed a black hole in the system. This hypothesis has not been confirmed due to a lack of direct observation but has generally been accepted from indirect evidence.