The Sun has been observed through a telescope for four centuries. However, its study made a prodigious leap at the end of the nineteenth century with the appearance of photography and spectroscopy, then at the beginning of the following century with the invention of the coronagraph and monochromatic filters, and finally in the second half of the twentieth century with the advent of large ground-based telescopes and space exploration. This article retraces the main stages of solar instrumental developments in Meudon, from its foundation by Jules Janssen in 1876 to the present day, limited to ground-based or balloon instrumentation, designed in Meudon and installed there or in other places (Nan{\c c}ay, Pic du Midi, Canary Islands). The Meudon astronomers played a pioneering role in the history of solar physics through the experimentation of innovative techniques. After the golden age of inventions, came the time of large instruments, studied in Meudon but often installed in more favourable sites, and that of space, in a framework of international collaboration, but this is not discussed here.
It is believed that the radio pulsars rotating at spin periods of about 30 millisecond or even lower got such high spins through the transfer of angular momentum by accreting matter from their binary companions (or past companions) in the past. Around 35% of MSPs are known to be isolated, some of the which might actually be in binaries - either not timed very well to obtain the signature of the orbit or in extremely wide binaries that can be revealed only through very accurate timing, as in the case of PSR J1024-0719. This has motivated an exercise to identify probable candidates of companions of MSPs in the Galactic field. This exercise has even the potential of discovering optical emission from MSPs themselves. Discovery of any possible binary companion will be followed by motivated pulsar timing campaigns to confirm the binary nature and to constrain orbital parameters.
We investigate angular momentum transport and accretion properties in a sample of protoplanetary discs with dynamical measurements of stellar masses, disc masses, and scale radii. From these data we infer effective $α$-viscosities, finding a remarkably broad range spanning over three orders of magnitude. This spread correlates with the stellar rotation period: systems with shorter periods exhibit significantly lower accretion rates, suggesting that they are undergoing at least temporary episodes of accretion bottleneck. We interpret this behaviour within the framework of magnetospheric accretion models, where the transition between steady accretion and the propeller regime is set by the relative locations of the co-rotation and magnetospheric radii. Our results indicate that stellar spin is a key parameter in regulating mass transfer from the disc to the star, and provide new evidence that the observed dispersion in $α$ reflects transitions between distinct accretion states rather than differences in global disc properties.
This chapter reviews proposed exoplanet biosignatures, including their biological origins, observable features, atmospheric sinks, and potentially confounding abiotic sources. Emphasis is placed on material published since past comprehensive reviews while providing a foundational understanding of each named biosignature. Topics include possible gaseous biosignatures (e.g., O$_2$, O$_3$, CH$_4$, N$_2$O, DMS, CH$_3$Cl, C$_5$H$_8$, NH$_3$, PH$_3$), surface biosignatures (e.g., vegetation red edge, other pigment features, polarization signatures), and temporal biosignatures (e.g., atmospheric seasonality). Potential frameworks for assessing remote biosignatures are described. Text and table summaries provide references to relevant original research articles.
Sanjay Gosain, Jack Harvey, Detrick Branson
et al.
Aging GONG second generation cameras (Silicon Mountain Design(TM) cameras) were planned to be replaced after their long service of more than a decade. This prompted a market-wide search for a potential replacement detector to meet the GONG science requirements. This report provides some history of the search process, a comparison between CMOS and CCD type sensors and then a quantitative evaluation of potential candidates to arrive at final selection. Further, a feasibility study of the selected sensor for adaptation to GONG optical system was done and sensor characteristics were independently verified in the laboratory. This technical report gives description of these studies and tests.
Sanjay Gosain, Jack Harvey, Valentin Martinez-Pillet
et al.
Designing compact instruments is the key for the scientific exploration by smaller spacecrafts such as cubesats or by deep space missions. Such missions require compact instrument designs to have minimal instrument mass. Here we present a proof of concept for miniaturization of the Global Oscillation Network Group GONG instrument. GONG instrument routinely obtains solar full disk Doppler and magnetic field maps of the solar photosphere using Ni 676 nm absorption line. A key concept for miniaturization of GONG optical design is to replace the bulky Lyot filter with a narrow-band interference filter and reduce the length of feed telescope. We present validation of the concept via numerical modeling as well as by proof of concept observations.
Abstract A characteristic property of pulsars is pulsed periodic radio emission, which has a high stability of periods. Despite the high stability of the emission periods of pulsars, monitoring the time of arrival of pulses (timing) shows the presence of different types of irregularities: variations of residual deviations, changes in the shape of the pulse, switching on and off of radio emission, and rotation discontinuities. Numerous observations of the radio emission of pulsars indicate that they are caused mainly by processes occurring in the pulsar’s magnetosphere. The special interest causes the observations of a pulsar in the Crab Nebula, performed, in particular, at Jodrell Bank and Pushchino Radio Astronomy Observatory of Lebedev Physical Institute. The connection between the scattering of radio pulses and the measure of the pulsar dispersion, which was established earlier in Pushchino together with Jodrell Bank, has been confirmed. The observed variations in the scattering of radio pulses and their partial correlation with the dispersion measure are explained by the eclipse of the pulsar by plasma clouds with electron density fluctuations significantly exceeding the corresponding fluctuations in the interstellar medium. The question of a possible connection between glitches, dispersion measure variations, radio pulses scattering, and gamma-ray flares is discussed.
One of the few ways that we can understand the environment around dusty stars and how much material they contribute back to the Universe, is by fitting their brightness at different wavelengths with models that account for how the energy transfers through the dust. The DESK is a python package designed to compare the best fits of different stellar samples and model grids for a better understanding of the results and their uncertainties. The package fits the Spectral Energy Distribution (SED) of evolved stars, using photometry or spectra, to grids of radiative transfer models using a least-squares method. The package includes newly created grids using a variety of different dust species, and state-of-the-art dust growth grids. A robust method for testing different model grids will be particularly important given the wealth of infrared data to come from the James Webb Space Telescope (JWST).
Data rates in an interstellar communication network suffer from the inverse square law due to the vast distances between the stars. To achieve high (Gbits/s) data rates, some combination of large apertures and high power is required. Alternatively, signals can be focused by the gravitational lenses of stars to yield gains of order $10^{9}$, compared to the direct path. Gravitational lens physics imposes a set of constraints on the sizes and locations of receivers and apertures. These characteristics include the minimum and maximum receiver size, the maximum transmitter size, and the heliocentric receiver distance. Optimal sizes of receivers and transmitters are of order meters. Such small devices allow for the capture of the main lobe in the beam while avoiding the temporal smearing which affects larger apertures. These and other properties can be used to describe the most likely parameters of a lensed communication network, and to determine exact position of communication nodes in the heliocentric reference frame.
Periodic comets of different dynamical groups with orbits at 2 - 5 AU still occasionally active. The observed dust activity of such objects can be connected with processes of water ice sublimation (MBCs) or crystallization of amorphous water ice (QHCs) as well as with external causes. No connections of cometary flares with cyclic variations of solar activity indexes were found. But some individual solar flares can affect the brightness of comets. Cometary objects in the main asteroid belt have a lower statistic of flares than comets at orbits like quasi-Hilda objects.
Magnetic activity and surface flows at different scales pertub radial velocity measurements. This affects the detectability of low-mass exoplanets. In these flows, the effect of supergranulation is not as well characterized as the other flows, and we wish to estimate its effect on the detection of Earth-like planets in the habitable zone of Sun-like stars. We produced time series of radial velocities due to oscillations, granulation, and supergranulation, and estimated the detection limit for a G2 star and a period of 300 days. We also studied in detail the behavior of the power when the signal of a 1 Mearth planet was superposed on the signal from the stellar flows. We find that the detection rate does not reach 100% except for the supergranulation level we assume, which is still optimistic, and for an excellent sampling. We conclude that with current knowledge, it is a very challenging task to find Earth twins around Sun-like stars with our current capabilities.
Kamber R. Schwarz, Richard Teague, Edwin A. Bergin
Line ratios for different transitions of the same molecule have long been used as a probe of gas temperature. Here we use ALMA observations of the N2H+ J~=~1-0 and J~=~4-3 lines in the protoplanetary disk around TW Hya to derive the temperature at which these lines emit. We find an averaged temperature of 39~K with a one sigma uncertainty of 2~K for the radial range 0.8-2'', significantly warmer than the expected midplane temperature beyond 0.5'' in this disk. We conclude that the N2H+ emission in TW Hya is not emitting from near the midplane, but rather from higher in the disk, in a region likely bounded by processes such as photodissociation or chemical reprocessing of CO and N2 rather than freeze out.
Accretion disks can be eccentric: they support $m=1$ modes that are global and slowly precessing. But whether the modes remain trapped in the disk---and hence are long-lived---depends on conditions at the outer edge of the disk. Here we show that in disks with realistic boundaries, in which the surface density drops rapidly beyond a given radius, eccentric modes are trapped and hence long-lived. We focus on pressure-only disks around a central mass, and show how this result can be understood with the help of a simple second-order WKB theory. We show that the longest lived mode is the zero-node mode in which all of the disk's elliptical streamlines are aligned, and that this mode decays coherently on the viscous timescale of the disk. Hence such a mode, once excited, will live for the lifetime of the disk. It may be responsible for asymmetries seen in recent images of protoplanetary disks.
There is growing evidence that brown dwarfs may be comparable to main-sequence stars in terms of their abundance. In this paper, we explore the prospects for the existence of life on Earth-like planets around brown dwarfs. We consider the following factors: (i) the length of time that planets can exist in the temporally shifting habitable zone, (ii) the minimum photon fluxes necessary for oxygenic photosynthesis, and (iii) the lower limits on the fluxes of ultraviolet radiation to drive prebiotic reactions ostensibly necessary for the origin of life. By taking these effects into consideration, we find that it is unlikely for brown dwarfs with masses $\lesssim 30 M_J$ to host habitable planets over geologically significant timescales. We also briefly discuss some of the major biosignatures that might arise on these planets, assess the likelihood of their detection, and highlight some avenues for further study.
We developed software for detection of variable stars using CCD photometry. It works with "varfind data" that could be exported after processing CCD frames using C-Munipack. Our goals were maximum automation and support of large fields of view with thousands of stars. The program chooses the comparison stars automatically, processes all time series using multiple comparison stars to get final light curves. Different filtering algorithms are used to reduce the impact of outlying points, imaging artifacts and low quality CCD frames without careful manual time series reduction. We implemented various variable detection indices and plotting two-channel diagrams of selected pair of indices and mean brightness of the star to distinguish variables from constant stars for further manual check of outlying points as variable candidates.
In this paper, we are going to introduce the Kottamia Astronomical Observatory, KAO, to the astronomical community. The current status of the telescope together with the available instrumentations is described. An upgrade stage including a new optical system and a computer controlling of both the telescope and dome are achieved. The specifications of a set of CCD cameras for direct imaging and spectroscopy are given. A grating spectrograph is recently gifted to KAO from Okayama Astrophysical Observatory, OAO, of the National Astronomical Observatories in Japan. This spectrograph is successfully tested and installed at the F/18 Cassegrain focus of the KAO 74" telescope.
We perform multi-dimensional, time-dependent radiation transfer simulations for hard X-ray and γ-ray emissions, following radioactive decays of 56Ni and 56Co, for two-dimensional delayed-detonation models of Type Ia supernovae (SNe Ia). The synthetic spectra and light curves are compared with the sensitivities of current and future observatories for an exposure time of 106 s. The non-detection of the γ-ray signal from SN 2011fe at 6.4 Mpc by SPI on board INTEGRAL places an upper limit on the mass of 56Ni of ≲ 1.0 M☉, independently from observations in any other wavelengths. Signals from the newly formed radioactive species have not yet been convincingly measured from any SN Ia, but future X-ray and γ-ray missions are expected to deepen the observable horizon to provide high energy emission data for a significant SN Ia sample. We predict that the hard X-ray detectors on board NuStar (launched in 2012) or ASTRO-H (scheduled for launch in 2014) will reach to SNe Ia at ∼15 Mpc, i.e., one SN every few years. Furthermore, according to the present results, the soft γ-ray detector on board ASTRO-H will be able to detect the 158 keV line emission up to ∼25 Mpc, i.e., a few SNe Ia per year. Proposed next-generation γ-ray missions, e.g., GRIPS, could reach to SNe Ia at ∼20–35 Mpc by MeV observations. Those would provide new diagnostics and strong constraints on explosion models, detecting rather directly the main energy source of supernova light.