Pub Date : 2008-12-17DOI: 10.1007/978-3-642-11250-8_16
D. Martinez-Delgado, R. J. Gabany, J. Peñarrubia, H. Rix, S. Majewski, I. Trujillo, M. Pohlen
{"title":"A Pilot Survey of Stellar Tidal Streams in Nearby Spiral Galaxies","authors":"D. Martinez-Delgado, R. J. Gabany, J. Peñarrubia, H. Rix, S. Majewski, I. Trujillo, M. Pohlen","doi":"10.1007/978-3-642-11250-8_16","DOIUrl":"https://doi.org/10.1007/978-3-642-11250-8_16","url":null,"abstract":"","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"93 1","pages":"163-170"},"PeriodicalIF":0.0,"publicationDate":"2008-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86710630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-12-17DOI: 10.1142/9781848164703_0012
T. Hartquist, S. Loo, S. Falle
In 1986 Alex Dalgarno published a paper entitled "Is Interstellar Chemistry Useful?" By the middle 1970s, and perhaps even earlier, Alex had hoped that astronomical molecules would prove to: possess significant diagnostic utility; control many of the environments in which they exist; stimulate a wide variety of physicists and chemists who are at least as fascinated by the mechanisms forming and removing the molecules as by astronomy. His own research efforts have contributed greatly to the realization of that hope. This paper contains a few examples of: how molecules are used to diagnose large-scale dynamics in astronomical sources including star forming regions and supernovae; the ways in which molecular processes control the evolution of astronomical objects such as dense cores destined to become stars and very evolved giant stars; theoretical and laboratory investigations that elucidate the processes producing and removing astronomical molecules and allow their detection.
{"title":"How Interstellar Chemistry (and Astrochemistry More Generally) Became Useful","authors":"T. Hartquist, S. Loo, S. Falle","doi":"10.1142/9781848164703_0012","DOIUrl":"https://doi.org/10.1142/9781848164703_0012","url":null,"abstract":"In 1986 Alex Dalgarno published a paper entitled \"Is Interstellar Chemistry Useful?\" By the middle 1970s, and perhaps even earlier, Alex had hoped that astronomical molecules would prove to: possess significant diagnostic utility; control many of the environments in which they exist; stimulate a wide variety of physicists and chemists who are at least as fascinated by the mechanisms forming and removing the molecules as by astronomy. His own research efforts have contributed greatly to the realization of that hope. This paper contains a few examples of: how molecules are used to diagnose large-scale dynamics in astronomical sources including star forming regions and supernovae; the ways in which molecular processes control the evolution of astronomical objects such as dense cores destined to become stars and very evolved giant stars; theoretical and laboratory investigations that elucidate the processes producing and removing astronomical molecules and allow their detection.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"144 1","pages":"129-143"},"PeriodicalIF":0.0,"publicationDate":"2008-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86201245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the context of f(R) theories of gravity, we study the cosmological evolution of scalar perturbations by using a completely general procedure. We find that the exact fourth‐order differential equation for the matter density perturbations in the longitudinal gauge, reduces to a second‐order equation for sub‐Hubble modes. This simplification is compared with the standard (quasi‐static) equation used in the literature. We show that for general f(R) functions the quasi‐static approximation is not justified. However for those f(R) adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it does give a correct description for the evolution of perturbations.
{"title":"Cosmological density perturbations in modified gravity theories","authors":"A. D. L. Cruz-Dombriz, A. Dobado, A. L. Maroto","doi":"10.1063/1.3141280","DOIUrl":"https://doi.org/10.1063/1.3141280","url":null,"abstract":"In the context of f(R) theories of gravity, we study the cosmological evolution of scalar perturbations by using a completely general procedure. We find that the exact fourth‐order differential equation for the matter density perturbations in the longitudinal gauge, reduces to a second‐order equation for sub‐Hubble modes. This simplification is compared with the standard (quasi‐static) equation used in the literature. We show that for general f(R) functions the quasi‐static approximation is not justified. However for those f(R) adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it does give a correct description for the evolution of perturbations.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"111 1","pages":"252-255"},"PeriodicalIF":0.0,"publicationDate":"2008-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76171721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
For microquasars, the one time when these systems exhibit steady and powerful jets is when they are in the hard state. Thus, our understanding of this state is key to learning about the disk/jet connection. Recent observational and theoretical results have led to questions about whether we really understand the physical properties of this state, and even our basic picture of this state is uncertain. Here, I discuss some of the recent developments and possible problems with our understanding of this state. Overall, it appears that the strongest challenge to the standard truncated disk picture is the detection of broad iron features in the X-ray spectra, and it seems that either there is a problem with the truncated disk picture or there is a problem with the relativistic reflection models used to explain the broad iron features.
{"title":"Hard (State) Problems","authors":"J. Tomsick","doi":"10.22323/1.062.0004","DOIUrl":"https://doi.org/10.22323/1.062.0004","url":null,"abstract":"For microquasars, the one time when these systems exhibit steady and powerful jets is when they are in the hard state. Thus, our understanding of this state is key to learning about the disk/jet connection. Recent observational and theoretical results have led to questions about whether we really understand the physical properties of this state, and even our basic picture of this state is uncertain. Here, I discuss some of the recent developments and possible problems with our understanding of this state. Overall, it appears that the strongest challenge to the standard truncated disk picture is the detection of broad iron features in the X-ray spectra, and it seems that either there is a problem with the truncated disk picture or there is a problem with the relativistic reflection models used to explain the broad iron features.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"67 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2008-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77380401","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-12-15DOI: 10.1051/0004-6361:200811084
I. Pérez, P. Sánchez-Blázquez, Almudena Zurita
This is the first paper of a series aimed to understand the formation and evolution of bars in early-type spirals and their influence in the evolution of the galaxy. Optical long-slit spectra along the major axis of the bar of a sample of 20 galaxies are analyzed. Line-strength indices in the bar region are measured to derive stellar mean-age and metallicity distributions along the bars using stellar population models. We find three different types of bars according to their metallicity and age distribution along the radius: 1) Bars with negative metallicity gradients. They show mean young/intermediate population (< 2 Gyr), and have amongst the lowest stellar maximum central velocity dispersion of the sample. 2) Bars with null metallicity gradients. These galaxies tend to have negative age gradients. 3) Bars with positive metallicity gradients. These galaxies are predominantly those with higher velocity dispersion and older mean population. We found no significant correlation between the age and metallicity distribution, and bar/galaxy parameters such as the AGN presence, size or the bar strength. From the kinematics, we find that all the galaxies show a disk-like central component. The results from the metallicity and age gradients indicate that most galaxies with high central stellar velocity dispersion host bars that could have been formed more than 3 Gyrs ago, while galaxies with lower central velocity dispersions show a wider distribution in their population and age gradients. A few bars show characteristics compatible with having been formed less than <2 Gy ago. These results place strong constrains to models of bar formation and evolution. The disk-like central components also show the important role played by bars in the secular evolution of the central structure.
{"title":"Study of the stellar line-strength indices and kinematics along bars","authors":"I. Pérez, P. Sánchez-Blázquez, Almudena Zurita","doi":"10.1051/0004-6361:200811084","DOIUrl":"https://doi.org/10.1051/0004-6361:200811084","url":null,"abstract":"This is the first paper of a series aimed to understand the formation and evolution of bars in early-type spirals and their influence in the evolution of the galaxy. Optical long-slit spectra along the major axis of the bar of a sample of 20 galaxies are analyzed. Line-strength indices in the bar region are measured to derive stellar mean-age and metallicity distributions along the bars using stellar population models. We find three different types of bars according to their metallicity and age distribution along the radius: 1) Bars with negative metallicity gradients. They show mean young/intermediate population (< 2 Gyr), and have amongst the lowest stellar maximum central velocity dispersion of the sample. 2) Bars with null metallicity gradients. These galaxies tend to have negative age gradients. 3) Bars with positive metallicity gradients. These galaxies are predominantly those with higher velocity dispersion and older mean population. We found no significant correlation between the age and metallicity distribution, and bar/galaxy parameters such as the AGN presence, size or the bar strength. From the kinematics, we find that all the galaxies show a disk-like central component. The results from the metallicity and age gradients indicate that most galaxies with high central stellar velocity dispersion host bars that could have been formed more than 3 Gyrs ago, while galaxies with lower central velocity dispersions show a wider distribution in their population and age gradients. A few bars show characteristics compatible with having been formed less than <2 Gy ago. These results place strong constrains to models of bar formation and evolution. The disk-like central components also show the important role played by bars in the secular evolution of the central structure.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2008-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75173384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Interactions between dark matter and dark energy with a given equation of state are known to modify the cosmic dynamics. On the other hand, the strength of these interactions is subject to strong observational constraints. Here we discuss a model in which the transition from decelerated to accelerated expansion of the Universe arises as a pure interaction phenomenon. Various cosmological scenarios that describe a present stage of accelerated expansion, like the ΛCDM model or a (generalized) Chaplygin gas, follow as special cases for different interaction rates. This unifying view on the homogeneous and isotropic background level is accompanied by a non‐adiabatic perturbation dynamics which can be seen as a consequence of a fluctuating interaction rate.
{"title":"Accelerated expansion through interaction","authors":"W. Zimdahl","doi":"10.1063/1.3141342","DOIUrl":"https://doi.org/10.1063/1.3141342","url":null,"abstract":"Interactions between dark matter and dark energy with a given equation of state are known to modify the cosmic dynamics. On the other hand, the strength of these interactions is subject to strong observational constraints. Here we discuss a model in which the transition from decelerated to accelerated expansion of the Universe arises as a pure interaction phenomenon. Various cosmological scenarios that describe a present stage of accelerated expansion, like the ΛCDM model or a (generalized) Chaplygin gas, follow as special cases for different interaction rates. This unifying view on the homogeneous and isotropic background level is accompanied by a non‐adiabatic perturbation dynamics which can be seen as a consequence of a fluctuating interaction rate.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"32 1","pages":"416-419"},"PeriodicalIF":0.0,"publicationDate":"2008-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79336871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Hanasz, K. Kowalik, D. W'olta'nski, R. Pawlaszek
We present a new multi-fluid, grid MHD code PIERNIK, which is based on the Relaxing TVD scheme (Jin & Xin, 1995). The original scheme (see Trac & Pen (2003) and Pen et al. (2003)) has been extended by an addition of dynamically independent, but interacting fluids: dust and a diffusive cosmic ray gas, described within the fluid approximation, with an option to add other fluids in an easy way. The code has been equipped with shearing-box boundary conditions, and a selfgravity module, Ohmic resistivity module, as well as other facilities which are useful in astrophysical fluid-dynamical simulations. The code is parallelized by means of the MPI library. In this paper we present an extension of PIERNIK, which is designed for simulations of diffusive propagation of the Cosmic-Ray (CR) component in the magnetized ISM.
{"title":"PIERNIK mhd code - a multi-fluid, non-ideal extension of the relaxing-TVD scheme (IV)","authors":"M. Hanasz, K. Kowalik, D. W'olta'nski, R. Pawlaszek","doi":"10.1051/eas/1256060","DOIUrl":"https://doi.org/10.1051/eas/1256060","url":null,"abstract":"We present a new multi-fluid, grid MHD code PIERNIK, which is based on the Relaxing TVD scheme (Jin & Xin, 1995). The original scheme (see Trac & Pen (2003) and Pen et al. (2003)) has been extended by an addition of dynamically independent, but interacting fluids: dust and a diffusive cosmic ray gas, described within the fluid approximation, with an option to add other fluids in an easy way. The code has been equipped with shearing-box boundary conditions, and a selfgravity module, Ohmic resistivity module, as well as other facilities which are useful in astrophysical fluid-dynamical simulations. The code is parallelized by means of the MPI library. In this paper we present an extension of PIERNIK, which is designed for simulations of diffusive propagation of the Cosmic-Ray (CR) component in the magnetized ISM.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"48 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2008-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77268571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present synthetic FeH band spectra in the z‐filter range for several M‐dwarf models with log g = 3.0–5.0 [cgs] and Teff = 2800 K–3450 K. Our aim is to characterize convective velocities in M‐dwarfs and to give a rough estimate of the range in which 3D‐atmosphere treatment is necessary and where 1D‐atmosphere models suffice for the interpretation of molecular spectral features. This is also important in order to distinguish between the velocity‐broadening and the rotational‐ or Zeeman‐broadening. The synthetic spectra were calculated using 3D CO5BOLD radiative‐hydrodynamic (RHD) models and the line synthesis code LINFOR3D. We used complete 3D‐models and high resolution 3D spectral synthesis for the detailed study of some well isolated FeH lines. The FeH line strength shows a dependence on surface gravity and effective temperature and could be employed to measure both quantities in M‐type objects. The line width is related to the velocity‐field in the model stars, which depends strongly on surface gravit...
{"title":"Teff and log g dependence of FeH in M‐dwarfs","authors":"S. Wende, A. Reiners, H. Ludwig","doi":"10.1063/1.3099241","DOIUrl":"https://doi.org/10.1063/1.3099241","url":null,"abstract":"We present synthetic FeH band spectra in the z‐filter range for several M‐dwarf models with log g = 3.0–5.0 [cgs] and Teff = 2800 K–3450 K. Our aim is to characterize convective velocities in M‐dwarfs and to give a rough estimate of the range in which 3D‐atmosphere treatment is necessary and where 1D‐atmosphere models suffice for the interpretation of molecular spectral features. This is also important in order to distinguish between the velocity‐broadening and the rotational‐ or Zeeman‐broadening. The synthetic spectra were calculated using 3D CO5BOLD radiative‐hydrodynamic (RHD) models and the line synthesis code LINFOR3D. We used complete 3D‐models and high resolution 3D spectral synthesis for the detailed study of some well isolated FeH lines. The FeH line strength shows a dependence on surface gravity and effective temperature and could be employed to measure both quantities in M‐type objects. The line width is related to the velocity‐field in the model stars, which depends strongly on surface gravit...","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"8 1","pages":"816-819"},"PeriodicalIF":0.0,"publicationDate":"2008-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75279417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dark energy is usually parametrized as a perfect fluid with negative pressure and a certain equation of state. Besides, it is supposed to interact very weakly with the rest of the components of the universe and, as a consequence, there is no reason to expect it to have the same large scale rest frame as matter and radiation. Thus, apart from its equation of state w and its energy density ΩDE one should also consider its velocity as a free parameter to be determined by observations. This velocity defines a cosmological preferred frame, so the universe becomes anisotropic and, therefore, the CMB temperature fluctuations will be affected, modifying mainly the dipole and the quadrupole.
{"title":"On the dark energy rest frame and the CMB","authors":"J. B. Jiménez, A. L. Maroto","doi":"10.1063/1.3141251","DOIUrl":"https://doi.org/10.1063/1.3141251","url":null,"abstract":"Dark energy is usually parametrized as a perfect fluid with negative pressure and a certain equation of state. Besides, it is supposed to interact very weakly with the rest of the components of the universe and, as a consequence, there is no reason to expect it to have the same large scale rest frame as matter and radiation. Thus, apart from its equation of state w and its energy density ΩDE one should also consider its velocity as a free parameter to be determined by observations. This velocity defines a cosmological preferred frame, so the universe becomes anisotropic and, therefore, the CMB temperature fluctuations will be affected, modifying mainly the dipole and the quadrupole.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"30 5 1","pages":"193-196"},"PeriodicalIF":0.0,"publicationDate":"2008-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77359822","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present the modeling of partial frequency redistribution (PRD) effects for the fluorescent emission lines of molecular hydrogen, the general computational approximations, and the applications to planetary atmospheres, as well as interstellar medium. Our model is applied to FUSE observations of Jupiter, Saturn, and reflection nebulae, allowing an independent confirmation of the H2 abundance and the structure of planetary atmospheres.
{"title":"Modeling H2 Fluorescence in Planetary Atmospheres with Partial Frequency Redistribution","authors":"R. Lupu, P. Feldman, S. McCandliss, K. France","doi":"10.1063/1.3154056","DOIUrl":"https://doi.org/10.1063/1.3154056","url":null,"abstract":"We present the modeling of partial frequency redistribution (PRD) effects for the fluorescent emission lines of molecular hydrogen, the general computational approximations, and the applications to planetary atmospheres, as well as interstellar medium. Our model is applied to FUSE observations of Jupiter, Saturn, and reflection nebulae, allowing an independent confirmation of the H2 abundance and the structure of planetary atmospheres.","PeriodicalId":8453,"journal":{"name":"arXiv: Astrophysics","volume":"200 1","pages":"228-230"},"PeriodicalIF":0.0,"publicationDate":"2008-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76034325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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