Spectroscopy of hot subdwarf binaries Kreuzer, Simon; Irrgang, Andreas; Heber, Ulrich
Open Astronomy,
06/2018, Letnik:
27, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present a status report of our spectroscopic analysis of subdwarf binaries consisting of a subdwarf and a F/G/K-type main-sequence companion. These systems selected from SDSS photometry show ...significant excess in the (infra-)red which can not be explained by interstellar reddening. Inspection of SDSS spectra revealed that most of them are composite spectrum sdB binaries. Once their spectra are disentangled, a detailed spectral analysis can be carried out. It reveals T
, log g and the metal abundance of each individual star. The cool companion is of particular interest, because its spectrum reveals the original chemical composition of the binary.
Context.
The ESA
Gaia
mission is a remarkable tool for stellar population analysis through its accurate Hertzsprung–Russell diagram. Its precise astrometry has propelled detailed kinematic studies of ...the Milky Way and the identification of high-velocity outliers.
Aims.
Motivated by the historical identification of runaway main-sequence (MS) stars of an early spectral type at high Galactic latitudes, we test the capability of
Gaia
at identifying new such stars.
Methods.
We selected ≈2300 sources with
Gaia
magnitudes of
G
BP
−
G
RP
≤ 0.05, which are compatible with the colors of low-extinction MS stars that are earlier than a mid-A spectral type, and obtained low-resolution optical spectroscopy for 48 such stars. By performing detailed photometric and spectroscopic analyses, we derived their atmospheric and physical parameters (effective temperature, surface gravity, radial velocity, interstellar reddening, spectrophotometric distance, mass, radius, luminosity, and age). The comparison between spectrophotometric and parallax-based distances enabled us to disentangle the MS candidates from older blue horizontal branch (BHB) candidates.
Results.
We identify 12 runaway MS candidates, with masses between 2 and 6
M
⊙
. Their trajectories were traced back to the Galactic disk in order to identify their most recent Galactic plane crossings and the corresponding flight times. All 12 candidates are ejected from the Galactic disk within 2 to 16.5 kpc from the Galactic center and possess flight times that are shorter than their evolutionary ages, which is compatible with a runaway hypothesis. Three MS candidates have ejection velocities exceeding 450 km s
−1
, thus, they appear to challenge the canonical ejection scenarios for late B-type stars. The fastest star of our sample also has a non-negligible Galactic escape probability if its MS nature can be confirmed. We identify 27 BHB candidates, and the two hottest stars in our sample are rare low-mass stars of late O- and early B-types, evolving towards the white dwarf cooling sequence.
Conclusions.
The combination of
Gaia
parallaxes and proper motions can lead to the efficient selection of runaway blue MS candidates up to 10 kpc away from the Sun. High resolution spectra are needed to confirm the MS status, via precise measurements of projected rotational velocities and chemical compositions.
Context. The ESA Gaia mission is a remarkable tool for stellar population analysis through its accurate Hertzsprung–Russell diagram. Its precise astrometry has propelled detailed kinematic studies of ...the Milky Way and the identification of high-velocity outliers. Aims. Motivated by the historical identification of runaway main-sequence (MS) stars of an early spectral type at high Galactic latitudes, we test the capability of Gaia at identifying new such stars. Methods. We selected ≈2300 sources with Gaia magnitudes of GBP − GRP ≤ 0.05, which are compatible with the colors of low-extinction MS stars that are earlier than a mid-A spectral type, and obtained low-resolution optical spectroscopy for 48 such stars. By performing detailed photometric and spectroscopic analyses, we derived their atmospheric and physical parameters (effective temperature, surface gravity, radial velocity, interstellar reddening, spectrophotometric distance, mass, radius, luminosity, and age). The comparison between spectrophotometric and parallax-based distances enabled us to disentangle the MS candidates from older blue horizontal branch (BHB) candidates. Results. We identify 12 runaway MS candidates, with masses between 2 and 6 M⊙. Their trajectories were traced back to the Galactic disk in order to identify their most recent Galactic plane crossings and the corresponding flight times. All 12 candidates are ejected from the Galactic disk within 2 to 16.5 kpc from the Galactic center and possess flight times that are shorter than their evolutionary ages, which is compatible with a runaway hypothesis. Three MS candidates have ejection velocities exceeding 450 km s−1, thus, they appear to challenge the canonical ejection scenarios for late B-type stars. The fastest star of our sample also has a non-negligible Galactic escape probability if its MS nature can be confirmed. We identify 27 BHB candidates, and the two hottest stars in our sample are rare low-mass stars of late O- and early B-types, evolving towards the white dwarf cooling sequence. Conclusions. The combination of Gaia parallaxes and proper motions can lead to the efficient selection of runaway blue MS candidates up to 10 kpc away from the Sun. High resolution spectra are needed to confirm the MS status, via precise measurements of projected rotational velocities and chemical compositions.
The triton in a finite volume Kreuzer, Simon; Hammer, H.-W.
Physics letters. B,
01/2011, Letnik:
694, Številka:
4-5
Journal Article
Recenzirano
Odprti dostop
Understanding the volume dependence of the triton binding energy is an important step towards lattice simulations of light nuclei. We calculate the triton binding energy in a finite cubic box with ...periodic boundary conditions to leading order in the pionless effective field theory. Higher order corrections are estimated and the proper renormalization of our results is verified explicitly. We present results for the physical triton as well as for the pion-mass dependence of the triton spectrum near the “critical” pion mass, Mπcrit≈197 MeV, where chiral effective field theory suggests that the nucleon–nucleon scattering lengths in the 1S0- and 3S1-channels diverge simultaneously. An extension of the Lüscher formula to the three-body system is implicit in our results.
The old Galactic halo population of stars is not only a glimpse into the history of the Galaxy but also provides access to an extensive amount of mass probes to unravel the total mass and shape of ...the gravitational potential of the Galaxy, especially its dark matter halo. This work studies all stars of a spectroscopic survey carried out at the 6.5m Multi-Mirror-Telescope (MMT), which explored the Galactic halo population. The most famous discovery in this survey were fast stars travelling at speeds that may even exceed the Galactic escape velocity - so-called Hypervelocity stars (HVSs). This work explores all targets in the MMT sample. Most of the objects are blue horizontal branch (BHB) stars, blue stragglers (BSs) and White Dwarfs (WDs). Atmospheric parameters have been determined for all but a few objects and, if possible, stellar parameters like masses and distances were inferred by constructing spectral energy distributions (SEDs) by the use of photometric measurements of a veriety of surveys. The distance was combined with Gaia DR2proper motions and the radial velocity from spectroscopy making the full six dimentional phase space information available. A subsequent kinematic analysis was carried out for the different populations. The tailored analysis strategy of this work allows unprecedented statements about the nature and origin of the HVSs in the MMT sample. The fastest ones are thought to be ejected from the Galactic centre by a slingshot mechanism during a close passage at the supermassive black hole (Hills mechanism). For almost all of the 18 targets with more or less well-constrained place of origin, however, the Galactic center is excluded as a possible place of ejection. This challenges our current picture of HVS acceleration mechanisms. HVS 22 with its current rest-frame velocity of 3grf = 1530+690 −530is the most extreme candidate. Unfortunately, it is not possible to constrain its place of origin with current data.A surprising discovery made in the course of this work is the identification of 29 B-type supergiants, 28 of which are located in the outskirts of M31, M33 and two other dwarf Galaxies in the local Group. All of them provide an excellent independent test for the spectrophotometric distances.For the first time, the BHB and BS population in the MMT survey can be separated based on high-precision atmopheric parameters. The analysis of the BHB population revealed, that assuming different helium abundance resolves inconsistencies in modeling the Grundahl jump – a discontinuity at 11500 K due to the onset of diffusion and radiative levitation.The WD mass distribution in the MMT sample is found to be consistent with literature, but high-mass WDs are missing due to the color selection critera of the sample. Furthermore, 101 new WDs are identified and 166 WDs previously listed as candidates receive atmospheric parameters.This work, furthermore, identifies 8 proper motion dominated BHB high-velocity star candidates and three extremely low mass (pre-ELM) WD candidates. Follow-up observations are required to confirm or deny their nature.
Efimov physics in a finite volume Kreuzer, Simon; Hammer, H.-W.
Physics letters. B,
03/2009, Letnik:
673, Številka:
4-5
Journal Article
Recenzirano
Odprti dostop
Three bosons with large scattering length show universal properties that do not depend on the details of the interaction at short distances. In the three-boson system, these properties include a ...geometric spectrum of shallow three-body states called “Efimov states” and log-periodic dependence of scattering observables on the scattering length. We investigate the modification of the Efimov states in a finite cubic box and calculate the dependence of their energies on the box size using effective field theory. We explicitly verify the renormalization of the effective field theory in the finite volume.
ABSTRACT PSR J1024-0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to a ...reexamination of its properties. We present updated radio timing observations along with new and archival optical data which show that PSR J1024-0719 is most likely in a long-period (2-20 kyr) binary system with a low-mass ( ), low-metallicity ( dex) main-sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, which is consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters.
Three particles with large two-body scattering lengths display universal properties including a spectrum of three-body bound states called “Efimov trimers”. I calculate the spectrum of three ...identical bosons inside a finite cubic box below the three-body breakup threshold. The dependence of the spectrum on the box size and the effects of the breakdown of spherical symmetry are investigated using effective field theory. The renormalization of the effective field theory in the finite volume is explicitly verified. The study of the three-nucleon system inside a finite cubic volume provides a tool for the understanding of Lattice QCD results. I study the triton in a finite volume at physical and unphysical pion masses.
Motivated by the historical identification of runaway main-sequence (MS) stars of early spectral type at high Galactic latitudes, we test the capability of Gaia at identifying new such stars. We have ...selected ~2300 sources with Gaia magnitudes of GBP - GRP < 0.05, compatible with the colors of low-extinction MS stars earlier than mid-A spectral type, and obtained low-resolution optical spectroscopy for 48 such stars. By performing detailed photometric and spectroscopic analyses, we derive their atmospheric and physical parameters (effective temperature, surface gravity, radial velocity, interstellar reddening, spectrophotometric distance, mass, radius, luminosity, and age). The comparison between spectrophotometric and parallax-based distances enables us to disentangle the MS candidates from older blue horizontal branch (BHB) candidates. We identify 12 runaway MS candidates, with masses between 2 and 6 Msun. Their trajectories are traced back to the Galactic disc to identify their most recent Galactic plane crossings and the corresponding flight times. All 12 candidates are ejected from the Galactic disc within 2 to 16.5 kpc from the Galactic center and possess flight times that are shorter than their evolutionary ages, compatible with a runaway hypothesis. Three MS candidates have ejection velocities exceeding 450 km/s, thus, appear to challenge the canonical ejection scenarios for late B-type stars. The fastest star of our sample also has a non-negligible Galactic escape probability if its MS nature can be confirmed. We identify 27 BHB candidates, and the two hottest stars in our sample are rare late O and early B type stars of low mass evolving towards the white dwarf cooling sequence.
Young massive stars in the halo are assumed to be runaway stars from the Galactic disk. Possible ejection scenarios are binary supernova ejections (BSE) or dynamical ejections from star clusters ...(DE). Hypervelocity stars (HVSs) are extreme runaway stars that are potentially unbound from the Galaxy. Powerful acceleration mechanisms such as the tidal disruption of a binary system by a supermassive black hole (SMBH) are required to produce them. Therefore, HVSs are believed to originate in the Galactic center (GC), the only place known to host an SMBH. The second Gaia data release (DR2) offers the opportunity of studying HVSs in an unprecedented manner. We revisit some of the most interesting high-velocity stars, that is, 15 stars for which proper motions with the Hubble Space Telescope were obtained in the pre-Gaia era, to unravel their origin. By carrying out kinematic analyses based on revised spectrophotometric distances and proper motions from Gaia DR2, kinematic properties were obtained that help constrain the spatial origins of these stars. Stars that were previously considered (un)bound remain (un)bound in Galactic potentials favored by Gaia DR2 astrometry. For nine stars (five candidate HVSs plus all four radial velocity outliers), the GC can be ruled out as spatial origin at least at \(2\sigma\) confidence level, suggesting that a large portion of the known HVSs are disk runaway stars launched close to or beyond Galactic escape velocities. The fastest star in the sample, HVS3, is confirmed to originate in the Large Magellanic Cloud. Because the ejection velocities of five of our non-GC stars are close to or above the upper limits predicted for BSE and DE, another powerful dynamical ejection mechanism (e.g., involving massive perturbers such as intermediate-mass black holes) is likely to operate in addition to the three classical scenarios mentioned above.
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