To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure no-reply@cambridge.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Many interacting binaries start their mass exchange when a donor overfilling its Roche lobe has evolved to a giant branch. The response of the donor's radius to the mass loss as compared to the response of its Roche lobe determines the fate of the binary system – whether it will proceed with a stable mass transfer, or experience dramatic common envelope event. Recent studies of responses of realistic giant's stellar models to a fast mass loss showed that this response is not purely adiabatic as previously thought but depends on the behavior of giant's superadiabatic surface layer. In this contribution, we explore in further details how an interplay between superadiabatic layer's thermal timescale and the dynamic timescale of the donor affects the donor's mass loss. We also find that the initiation of the mass loss causes mass loss induced pulsations.
From theoretical analysis and site testing work for 4 years on Dome A, Antarctica, we can reasonably predict that it is a very good astronomical site, as good as or even better than Dome C and suitable for observations ranging from optical to infrared & sub-mm wavelengths. After the Chinese Small Telescope ARray (CSTAR), which was composed of four small fixed telescopes with diameter of 145mm and the three Antarctic Survey Telescopes (AST3) with 500mm entrance diameter, the Kunlun Dark Universe Survey Telescope (KDUST) with diameter of 2.5m is proposed. KDUST will adopt an innovative optical system which can deliver very good image quality over a 2 square degree flat field of view. Some other features are: a fixed focus suitable for different instruments, active optics for miscollimation correction, a lens-prisms that can be used as an atmospheric dispersion corrector or as a very low-dispersion spectrometer when moved in / out of the main optical path without changing the performance of the system, and a compact structure to make easier transportation to Dome A. KDUST will be mounted on a tower with height 15m in order to make a full use of the superb free atmospheric seeing.
We model the large-scale Galactic magnetic fields, including a spiral arm compression to generate anisotropic turbulence, by comparing polarized synchrotron and thermal dust emission. Preliminary results show that in the outer Galaxy, the dust emission comes from regions where the fields are more ordered than average while the situation is reversed in the inner Galaxy. We will attempt in subsequent work to present a more complete picture of what the comparison of these observables tells us about the distribution of the components of the magnetized ISM and about the physics of spiral arm shocks and turbulence.
The search for B-mode, or curl-type, polarization in the Cosmic Microwave Background is the most promising technique to constrain or detect primordial gravitational waves predicted by the theory of inflation. The Bicep telescope, which observed from the South Pole for three years from 2006 through 2008, is the first experiment specifically designed to target this signal. We review the observational motivations for inflation, the advantages of B-mode observations as a technique for detecting the gravitational wave background, and the design features of Bicep that optimize it for this search. The final analysis of all three seasons of Bicep data is in progress, representing a 50% increase in integration time compared to the result from Chiang et al. (2010). A preview of the three year result includes E-mode and B-mode maps, as well as the projected constraint on r, the tensor-to-scalar ratio.
We have been carrying out a systematic survey of the star formation and ISM properties in the host galaxies of z∼6 quasars. Our 250 GHz observations, together with available data from the literature, yield a sample of 14 z∼6 quasars that are bright in millimeter dust continuum emission with estimated FIR luminosities of a few 1012 to 1013 L⊙. Most of these millimeter-detected z∼6 quasars have also been detected in molecular CO line emission, indicating molecular gas masses on order of 1010 M⊙. We have searched for [C II] 158 micron fine structure line emission toward four of the millimeter bright z∼6 quasars with ALMA and all of them have been detected. All these results suggest massive star formation at rates of about 600 to 2000 M⊙ yr−1 over the central few kpc region of these quasar host galaxies.
Recent observations have provided evidence that the solar photospheric magnetic fields could have rapid and permanent changes in both longitudinal and transverse components associated with large (X- or M-class) solar flares. However, few observations have been reported about small flares. In this paper we find the observational evidence of changing photospheric vector magnetic fields associated with a B4.2-class flare obtained with the Solar Magnetic Field Telescope (SMFT) installed at Huairou Solar Observing Station (HSOS) of Nation Astronomical Observatories of Chinese Academy of Sciences.
Based on radial velocity data and Hipparcos proper motions, we present a new determination of the Galactocentric distance based on a purely kinematic model. We have selected three subgroups of Galactic thin-disk components (O–B5 stars, classical Cepheids and Galactic open clusters) to trace the local structure and kinematics of the Galactic disk. Adopting the approximation of axisymmetric circular rotation, we have derived the Sun's distance to the Galactic Center, R0 = 8.25 ± 0.79 kpc based on O–B5 stars, R0 = 7.98 ± 0.79 kpc based on Galactic Cepheids and R0 = 8.03 ± 0.70 kpc using open clusters, all of which are in excellent agreement with the current-best estimate of the Galactocentric distance.
With outdoor lighting ordinances in Arizona first in place around observatories in 1958 and 1972, then throughout the state since 1986, Arizonans have extensive experience working with communities and businesses to preserve our dark skies. Though communities are committed to the astronomy sector in our state, astronomers must collaborate with other stakeholders to implement solutions. Ongoing education and public outreach is necessary to enable ordinance updates as technology changes. Despite significant population increases, sky brightness measurements over the last 20 years show that ordinance updates are worth our efforts as we seek to maintain high quality skies around our observatories. Collaborations are being forged and actions taken to promote astronomy for the longer term in Arizona.
Interactions and mergers of gas-rich galaxies are important drivers of galaxy evolution, in particular in reshaping spirals and fueling powerful starbursts and supermassive nuclear black holes. Hubble Space Telescope observations of nuclei in merging galaxies have shown an increasing nuclear luminosity density in the optical/near-infrared light with advancing merger stage (Laine et al. 2003, Rossa et al. 2007, Veilleux et al. 2009, Haan et al. 2011a), suggesting an increase of nuclear starburst activity. To address the physical conditions in major mergers and excitation mechanisms such as shocks and starbursts, it is necessary to resolve the spatial variations of the warm dust, molecular gas, and ionized gas on subgalactic scales. Here we summarize the main results based on Spitzer IRS spectral mapping observations of a sample of eight nearby, IR-bright galaxies of the Toomre Sequence (Toomre & Toomre 1972) that span the range from early through mid- to late-stage major mergers (Haan et al. 2011b).
We find that the cold molecular gas component as observed in the CO emission line does not correlate with the warm gas in early merger systems, leading to large spatial variations in the ratio of cold-to-warm molecular gas. In particular, the cold molecular gas distribution in NGC 4676 and NGC 6621 show a significant offset not only from the warm gas component, but also from the stellar (NIR) and dust distribution (PAH, mid-IR continuum). On locally resolved scales within a merger, we find an intrinsic relation between H2 and PAH flux as given by a power law with a very similar exponent (0.61 ± 0.05) for all galaxies but with a constant that can vary up to a factor of ten between different galaxies. These findings suggest a common dominant excitation mechanism for H2 emission over a large range of global H2/PAH flux ratios in major mergers. The spatial extent of the warm gas component (H2) is larger than for the PAH emission (in all galaxies but more extrem in mid-stage merger), which leads to an increase of the H2/PAH ratio as function of radius. Two merger systems (NGC 7592 and NGC 6621) show evidence for buried star formation in overlap regions between the nuclei, namely strong PAH, [Ne II], [Ne III] and warm gas (H2) emission, but no apparent corresponding CO (J = 1−0) emission. Our findings also demonstrate that the variations of the physical conditions within a merger are much larger than any systematic trends along the Toomre Sequence.
ASTEP (Antarctic Search for Transiting Exo Planets) is a research program funded mainly by French ANR grants and by the French Polar Institute (IPEV), dedicated to the photometric study of exoplanetary transits from Antarctica.
The preliminary “pathfinder” instrument ASTEP–South is described in another communication (Crouzet et al., these proceedings), and we focus in this presentation on the main instrument of the ASTEP program: “ASTEP–400”, a 40 cm robotized and thermally-controlled photometric telescope operated from the French-Italian Concordia station (Dome C, Antarctica).
ASTEP–400 has been installed at Concordia during the 2009-2010 summer campaign. Since, the telescope has been operated in nominal conditions during 2010 and 2011 winters, and the 2012 winterover is presently in progress. Data from the first two winter campaigns are available and processed. We give a description of the ASTEP–400 telescope from the mechanical, optical and thermal point of view. Control and software issues are also addressed. We end with a discussion of some astronomical results obtained with ASTEP–400.
The 2nd Fermi-LAT pulsar catalog includes 117 γ-ray pulsars, of which roughly one third are millisecond pulsars (MSPs) while the remaining two thirds split evenly into young radio-loud and radio-quiet pulsars. Although this large population will enable future, detailed studies of emission mechanisms and the evolution of the underlying neutron star population, some nearly-universal properties are already clear and unequivocal. We discuss some of these aspects below, including the altitude of the γ-ray emission site, the shape of the γ-ray spectrum, and the implications of the latter for the radiation mechanism.
It seems that in the past decade, there have been two paradigm shifts regarding star clusters. Firstly, the observational evidence for multiple stellar populations requires more extended and often complex star formation histories in star clusters. Secondly, theoretical models that form globular clusters in dwarf galaxies that are accreted at very early epochs (z > 5) are able to reproduce the age-metallicity relations observed. For the accretion scenario to be viable, globular clusters should also resemble the chemistry of at least some dwarf galaxies.
Helicity characteristics in active regions (ARs) are studied, using so far the most accurate vector magnetic field measurements obtained with SP/Hinode. Our sample includes all ARs observed by SP/Hinode, up to June 2012. The sample is divided into three sub-samples: Cycle 23 (from 2006.11 to 2008.06), Cycle 24a (from 2008.10 to 2010.09) and Cycle 24b (from 2010.10 to 2012.06). We confirm our previous findings that the usual hemispheric helicity sign rule is not obeyed in the descending phase of solar cycle 23 and is obeyed in the ascending phase of solar cycle 24. And we find that the second phase of the solar cycle 24 (Cycle 24b) shows an even stronger evidence of the usual hemispheric helicity sign rule than its first phase (Cycle 24a). It is also found that our previous finding that the strong and weak fields possess the opposite helicity signs is not followed in Cycle 24b, whereas it is weakly followed in Cycle 24a and strongly followed in the descending phase of Cycle 23. This means that this rule also has a solar cycle variation, in addition to the solar cycle variation of the usual hemispheric helicity sign rule, and there is a roughly 2-years time delay between the two.
As cities around the world grow more and more diverse, we must take this diversity into account in developing outreach activities and materials. The International Year of Astronomy in 2009 brought a lot of attention to the needs of underserved communities and developing countries, emphasizing the ideal of widespread access to astronomy outreach. Increasingly, however, we find that some of the same challenges facing underserved communities and developing countries are also present in modern metropolises. Conveniently, the linguistic and cultural diversity of our cities is more and more accurately reflected among the astronomy community. The diversity of the astronomical community itself creates opportunities for effective multicultural, multilingual outreach.
186 binary pulsars are shown in the magnetic field versus spin period (B-P) diagram, and their relations to the millisecond pulsars can be clearly seen. We declaim a minimum accretion rate for the millisecond pulsar formation both from the observation and theory. If the accretion rate is lower than the minimum accretion rate, the pulsar in binary system will not become a millisecond pulsar after the evolution.
We present radial-velocity measurements (RV) obtained in one of the numbers of programs underway to search for extrasolar planets with the spectrograph SOPHIE at the 1.93-m telescope of the Observatoire de Haute-Provence. Targets were selected from catalogs observed with ELODIE, which had been mounted previously at the telescope, in order to detect long-period planets with an extended database close to 15 years.
Evidence is now compelling that most externally-polluted white dwarfs derive their heavy atoms by accretion from asteroids – the building blocks of rocky planets. Optical and ultraviolet spectroscopy of a small sample of suitable white dwarf stars shows that to zeroth order, the accreted extrasolar parent bodies compositionally resemble bulk Earth. (1) Extrasolar planetesimals are at least 85% by mass composed of O, Mg, Si and Fe. (2) Compared to the Sun, C is often deficient, usually by at least a factor of 10 and therefore comprises less than 1% of an extrasolar planetesimal's mass. At least to-date, C has never been found to be enhanced as would be expected if carbon-rich planetesimals have formed. (3) While there may be individual exceptions, considered as a whole, the population of extrasolar asteroids accreted onto a well-defined sample of local white dwarf stars is less than 1% water by mass.
We performed the observation of the flux densities of Sgr A* at 90 and 102 GHz on 6 April 2005 using the Nobeyama Millimeter Array in order to detect the time lag between these frequencies. We constructed light curves covering a few hour with 1 min bin, and the Intra-Day Variability, which had a rising phase and intensity peak, of Sgr A* is clearly seen at both frequencies. We calculated the z-transformed discrete correlation function between the light curves of Sgr A* at 90 and 102 GHz. The derived time lag of the flares at these frequencies was approximately zero, contrary to our expectations based on the previously reported time lag at lower frequencies. If the radio flares of Sgr A* are explained by the expanding plasma model, the light curve at 90 GHz would be delayed with respect to the one at 102 GHz. However, we could not find such a delay with statistical significance in our data.
Today has been known for a considerable number of cases, the explosion of large meteoroids in Earth's atmosphere. This is confirmed by the data of registrations of fireballs by devices and the results of measurements in the atmosphere of bright light flashes by photodiodes Corporation “Sandia Laboratories", which were installed on geostationary satellites of the United States, and also by data of measurements of acoustic-gravitational waves from the thermal explosions of meteoroids [ReVelle D.O. Historical detection of atmospheric impacts by large bolides using acoustic-gravity waves, Near-Earth Objects, Ed. Remo J. Annals of the New York Academy of Sciences 882, 284-302, 1997]. The work [Brown P., Spalding R.E., ReVelle D.O. et al. The flux of small near-Earth objects colliding with the Earth, Nature 420, 314-316, 2002.] shows the results of processing the observations of flashes of large meteoroids in Earth's atmosphere, obtained with the help of geostationary satellites of the United States. Over 8.5 years (from February 1994 to September 2002) 300 such events were registered. On July 6, 2002 r over the Mediterranean Sea a bright fireball was registered. The energy of the meteoroid explosion that caused the phenomenon of the car, was 26 kilotons of TNT [Brown et al., 2002]. We believe that this energy refers to the height of the full bracking of the meteoroid. At a speed of 20.3 km/s adopted by the authors, body mass at this height is 5 × 108 g, and when entering the Earth's atmosphere, it was about 7 × 108 g. Based on the obtained values of the mass, we conclude that the exploded meteoroid, causing a phenomenon of the fireball was a fragment of the comet nucleus. In processing the density of the body were taken 1 g/cm3 and the initial velocity (~30 km/s).
In this study, we probe for the first time the molecular gas physical properties of several star forming regions located in the arms and inter-arms of the spiral galaxy NGC 6946. Combining our observations with additional data found in the literature, we provide in this study the most complete CO ladder ever obtained in these inter-arm and arm regions, i.e. the CO(1-0, 2-1, 3-2, 4-3, 6-5) and 13CO(1-0, 2-1) transitions. For each region studied, we use more precisely the large velocity gradient (LVG) assumption in order to derive the beam-averaged molecular gas physical properties. Namely, we obtained the gas kinetic temperature (i.e. 'best' TK), volume number gas density (i.e. 'best' n(H2)) and CO column density (i.e. 'best' N(CO)) which best reproduce the data for 8 regions investigated. Optical depths were also estimated for a large variety of CO lines in these regions. To identify the best values found, we used two complementary theoretical approaches when comparing the model predictions with the observations, i.e. the χ2 minimisation and the likelihood. Very different physical conditions for the molecular gas from a region to another have been obtained: TK ranges from 10 to 250 K, n(H2) ranges from 102.3 to 107.0 cm−3 and N(CO) ranges from 1015.0 to 1019.3 cm−2 among the arm and inter-arm regions. For each region probed, we also published for the first time the CO spectral line energy distribution (SLED) from CO(1-0) to CO(10-9) for this galaxy, mixing observations and model predictions which provide an essential insight for future follow-up observational programmes. Finally, in this work, we discuss the physical properties we obtained for each region in relation with the presence of young stellar population characteristics such as supernovae remnants (SNRs), Hi holes, Hii regions.