54200839
Momentum dependence of the phi-meson nuclear transparency
The production of phi mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the phi -> K+K- decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these targets over the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the value of the extracted phi width, which corresponds to an effective phi-N absorption cross section in the range of 14 - 21 mb.
121039239
Identification of K+-mesons from subthreshold pA collisions with ANKE at COSY-Jülich
Abstract The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Julich in spring 1998. An initial scientific goal is to study K + -production in pA collisions at subthreshold energies far below the free NN-threshold at T p =1.58 GeV. This requires the identification of K + -mesons in a background of pions and protons, about 10 6 times more intense. In this paper the sophisticated detection system and the software procedures for kaon identification are described. With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d 2 σ/ d Ω d p for deep subthreshold K + production at beam energies down to T p =1.0 GeV.
7502590
Inclusive K+-meson production in proton-nucleus interactions
Abstract.The production of K+-mesons in pA (A = D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-Jülich for beam energies Tp = 1.0-2.3 GeV. Double differential inclusive pC cross-sections at forward angles ϑ{K^+} < 12° as well as the target mass dependence of the K+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at TNN = 1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target mass dependence of the cross-sections at higher energies, the repulsive in-medium potential of the K+-mesons can be deduced. Using pN cross-section parameterisations from the literature and our measured pD data we derive a cross-section ratio σ(pn↦K+X)/σ(pp↦K+X) ∼ (3-4).
119445528
Vector and tensor analysing powers in deuteron-proton breakup reactions at intermediate energies
Abstract Vector and tensor analysing powers of the d → p → ( p p ) n (charge-exchange) and d → p → ( p n ) p (non-charge-exchange) breakup reactions have been measured with the ANKE spectrometer at the COSY ring at a deuteron beam energy of 1170 MeV for small momentum transfers to the low excitation energy ( p p ) or ( p n ) systems. A quantitative understanding of the values of A x x and A y y for the charge-exchange reaction is provided by impulse approximation calculations. The data suggest that spin-flip isospin-flip transitions, which dominate the charge-exchange breakup of the deuteron, are also important in the non-charge-exchange reaction.
56319302
THE FORWARD DETECTOR OF THE ANKE SPECTROMETER. SCINTILLATION AND CHERENKOV HODOSCOPES
Central Institute for Nuclear Research, Rossendorf, GermanyThe scintillation and Cherenkov counter system of the forward detector of ANKE, magnetic spec-trometer at the internal beam of the accelerator COSY in Jeulich, is described. The timing and amplitudecharacteristics are presented as well as the capabilities to select physical processes of interest.¶¨¸O¢ ¥E¸O ¸¨¸E¥³ ¸I¨´E¨²²O I¨µ´´OI ¨ I¥·¥´±µ¢¸±¨I ¸I¥EI¨±µ¢ ¶¥·¥¤´¥£µ ¤¥E¥±Eµ· ANKE, ³ £´¨E´µ£µ ¸¶¥±E·µ³¥E· ´ ¢´EE·¥´´¥³ ¶EI±¥ E¸±µ·¨E¥²O COSY ¢ ²¨I¥. ·¨¢¥¤¥´O¨I ¢·¥³¥´´O¥ ¨ ³¶²¨EE¤´O¥ I · ±E¥·¨¸E¨±¨, E ±¦¥ ¢µ§³µ¦´µ¸E¨ ¨I ¶·¨³¥´¥´¨O ¤²O ¢O¤¥²¥´¨O¨´E¥·¥¸EOÐ¨I E¨§¨I¥¸±¨I ¶·µI¥¸¸µ¢.
118789979
Measurement of Subthreshold K+ Production in pA Collisions with ANKE
15677079
Planetary companion candidates around the K giant stars 42 Draconis and HD 139 357
Context. For the past 3 years we have been monitoring 62 K giant stars using precise stellar radial velocity (RV) measurements with the 2 m Alfred Jensch Telescope of the Thuringer Landessternwarte Tautenburg ( TLS ). Aims. To probe the dependence of planet formation on stellar mass by finding planets around intermediate-mass giant stars. Methods. We present high accuracy RV measurements of the K1.5 III star 42 Dra and the K4 III star HD 139357. The wavelength reference for the RV measurements was provided by an iodine absorption cell placed in the optical path of the spectrograph. Results. Our measurements reveal that the time series of the radial velocity of 42 Dra shows a periodic variation of 479.1 days with a semiamplitude of K  = 112.5 m s -1 . An orbital solution yields a mass function of $f(m)$ = (5.29 ± 0.62) $\times$ 10 -8  solar masses ($M_{\odot}$) and an eccentricity of e  = 0.38  ±  0.06. From our template spectra, taken without the iodine cell, we determine a metallicity of -0.46  ±  0.04 dex and a stellar mass of 0.98 ± 0.06 $M_{\odot}$ for this star. HD 139 357 shows periodic RV variations of 1125.7 days with a semiamplitude K  = 159.9 m s -1 . An orbital solution yields an eccentricity, e = 0.10 ± 0.02 and mass function, $f(m)$ = (4.79 ± 0.57) $\times$ 10 -7  $M_{\odot}$. An iron abundance of -0.13 ± 0.04 dex is obtained, and a stellar mass of 1.31 ± 0.24 $M_{\odot}$ for the parent star is derived. An analysis of the HIPPARCOS photometry as well as our H α core flux measurements reveal no variability with the radial velocity period. Keplerian motion is the most likely explanation for the observed radial velocity variations for these stars. Conclusions. The K giant stars 42 Dra and HD 139 357 host extrasolar planets with “minimum masses” of 3.88 ± 0.85 Jupiter masses $M_{\mathrm{Jup}}$ and 9.76 ± 2.15 $M_{\mathrm{Jup}}$, respectively.
11989684
Line-profile tomography of exoplanet transits - II. A gas-giant planet transiting a rapidly rotating A5 star
Most of our knowledge of extrasolar planets rests on precise radial-velocity measurements, either for direct detection or for confirmation of the planetary origin of photometric transit signals. This has limited our exploration of the parameter space of exoplanet hosts to solar- and later-type, sharp-lined stars. Here we extend the realm of stars with known planetary companions to include hot, fast-rotating stars. Planet-like transits have previously been reported in the light curve obtained by the SuperWASP survey of the A5 star HD 15082 (WASP–33; V= 8.3, v sin i= 86 km s−1). Here we report further photometry and time-series spectroscopy through three separate transits, which we use to confirm the existence of a gas-giant planet with an orbital period of 1.22 d in orbit around HD 15082. From the photometry and the properties of the planet signal travelling through the spectral line profiles during the transit, we directly derive the size of the planet, the inclination and obliquity of its orbital plane and its retrograde orbital motion relative to the spin of the star. This kind of analysis opens the way to studying the formation of planets around a whole new class of young, early-type stars, hence under different physical conditions and generally in an earlier stage of formation than in sharp-lined late-type stars. The reflex orbital motion of the star caused by the transiting planet is small, yielding an upper mass limit of 4.1 MJupiter on the planet. We also find evidence of a third body of substellar mass in the system, which may explain the unusual orbit of the transiting planet. In HD 15082, the stellar line profiles also show evidence of non-radial pulsations, clearly distinct from the planetary transit signal. This raises the intriguing possibility that tides raised by the close-in planet may excite or amplify the pulsations in such stars.
119282381
Exoplanets around G-K Giants
G and K giants are a class of radial velocity (RV) variables. One reason for this variability are planetary companions which are indicated in time series of stellar spectra. Since 2004 these spectra in the visual range were obtained with the high resolution coud\'e \'echelle spectrograph mounted on the 2m telescope of the Th\"uringer Landessternwarte Tautenburg (TLS) for a northern sample of 62 very bright K giants. In the South around 300 G and K giants were observed with HARPS mounted on the 3.6m telescope on La Silla. The TLS sample contains at least 11 stars (18 %) which show low-amplitude, long-period RV variations most likely due to planets. This percentage of planet frequency is confirmed by preliminary results of the HARPS study. Moreover the TLS survey seems to indicate that giant planets do not favour metal-rich stars, are more massive, and have longer periods than those found around solar-type host stars.
23202373
Planetary transit candidates in the CoRoT LRa01 field
Context. The space mission CoRoT is devoted to the analysis of stellar variability and the photometric detection of extrasolar planets. Aims. We present the list of planetary transit candidates detected in the first short run observed by CoRoT that targeted SRc01, towards the Galactic center in the direction of Aquila, which lasted from April to May 2007. Methods. Among the acquired data, we analyzed those for 1269 sources in the chromatic bands and 5705 in the monochromatic band. Instrumental noise and the stellar variability were treated with several detrending tools, to which several transit-search algorithms were subsequently applied. Results. Fifty-one sources were classified as planetary transit candidates and 26 were followed up with ground-based observations. Until now, no planet has been detected in the CoRoT data from the SRc01 field.