119206485
Mapping the three-dimensional multi-band extinction and diffuse interstellar bands in the Milky Way with LAMOST
With modern large scale spectroscopic surveys, such as the SDSS and LSS-GAC, Galactic astronomy has entered the era of millions of stellar spectra. Taking advantage of the huge spectroscopic database, we propose to use a "standard pair" technique to a) Estimate multi-band extinction towards sightlines of millions of stars; b) Detect and measure the diffuse interstellar bands in hundreds of thousands SDSS and LAMOST low-resolution spectra; c) Search for extremely faint emission line nebulae in the Galaxy; and d) Perform photometric calibration for wide field imaging surveys. In this contribution, we present some results of applying this technique to the SDSS data, and report preliminary results from the LAMOST data.
119225915
The LEGUE high latitude bright survey design for the LAMOST pilot survey
We describe the footprint and input catalog for bright nights in the LAMOST Pilot Survey, which began in October 2011. Targets are selected from two stripes in the north and south Galactic Cap regions, centered at delta = 29 degrees, with 10 degrees width in declination, covering right ascensions of 135 degrees to 290 degrees and -30 degrees to 30 degrees respectively. We selected spectroscopic targets from a combination of the SDSS and 2MASS point source catalogs. The catalog of stars defining the field centers (as required by the Shack-Hartmann wavefront sensor at the center of the LAMOST field) consists of all V < 8(m) stars from the Hipparcos catalog. We employ a statistical selection algorithm that assigns priorities to targets based on their positions in multidimensional color/magnitude space. This scheme overemphasizes rare objects and de-emphasizes more populated regions of magnitude and color phase space, while ensuring a smooth, well-understood selection function. A demonstration of plate design is presented based on the Shack-Hartmann star catalog and an input catalog that was generated by our target selection routines.
118328964
SUBSTRUCTURE IN BULK VELOCITIES OF MILKY WAY DISK STARS
We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the midplane as well as azimuthally. These findings are based on Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic velocities for a sample of ~400, 000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun's radius and ±2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.
118527168
Detections of diffuse interstellar bands in the SDSS low-resolution spectra
Diffuse interstellar bands (DIBs) have been discovered for almost a century, but their nature remains one of the most challenging problems in the astronomical spectroscopy. Most recent work to identify and investigate the properties and carriers of DIBs concentrates on highresolution spectroscopy of selected sight-lines. In this paper, we report detections of DIBs in the Sloan Digital Sky Survey (SDSS) low-resolution spectra of a large sample of Galactic stars. Using a template subtraction method, we have successfully identified the DIBs λλ5780, 6283 in the SDSS spectra of a sample of about 2000 stars and measured their strengths and radial velocities. The sample is by far the largest ever assembled. The targets span a large range of reddening, E(B − V) ∼ 0.2–1.0, and are distributed over a large sky area and involve a wide range of stellar parameters (effective temperature, surface gravity and metallicity), confirming that the carriers of DIBs are ubiquitous in the diffuse interstellar medium (ISM). The sample is used to investigate relations between strengths of DIBs and magnitudes of line-of-sight extinction, yielding results [i.e. EW(5780) = 0.61 × E(B − V) and EW(6283) = 1.26 × E(B − V)] consistent with previous studies. DIB features have also been detected in the commissioning spectra of the Guoshoujing Telescope [the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)] of resolving power similar to that of the SDSS. Detections of DIBs of hundreds of thousands of stars are expected from the on-going and up-coming large-scale spectroscopic surveys such as Radial Velocity Experiment, SDSS III and LAMOST, particularly from the LAMOST Digital Sky Survey of the Galactic Anticentre (DSS-GAC). Such a huge data base will provide an unprecedented opportunity to study the demographical distribution and nature of DIBs as well as using DIBs to probe the distribution and properties of the ISM and the dust extinction.
118587112
Extremely metal-poor star candidates in the SDSS
For a sample of metal-poor stars ( 3.3 � (Fe/H) � 2.2) that have high- resolution spectroscopic abundance determinations, we have measured equivalent widths of the Ca II K, Mg I b and near-infrared Ca II triplet lines using low-resolution spectra from the Sloan Digital Sky Survey (SDSS), calculated effective temperatures from (g z)0 color, deduced stellar surface gravities by fitting stellar isochrones, and determined metallicities based on the aforementioned quantities. Metallicities thus derived from the Ca II K line are in much better agreement with the results deter- mined from high-resolution spectra than the values given in the SDSS Data Release 7. The metallicities derived from the Mg I b lines have a large dispersion owing to the large measurement errors, whereas those deduced from the Ca II triplet lines are too high due to both non-local thermodynamical equilibrium (NLTE) effects and mea- surement errors. Abundances after correction for the NLTE effect for the Mg I b lines and Ca II triplet lines are also presented. Following this method, we have identified six candidates of ultra-metal-poor stars with (Fe/H) � 4.0 from a sample of 166 metal-poor star candidates. One of them, SDSS J102915+172927, was recently con- firmed to be an ultra-metal-poor ((Fe/H) < 4.0) star with the lowest metallicity ever measured. Follow-up high-resolution spectroscopy for the other five ultra-metal-poor stars in our sample will therefore be of great interest.
119187574
Gamma-Ray Burst Spectrum with Decaying Magnetic Field
In the internal shock model for gamma-ray bursts (GRBs), the synchrotron spectrum from the fast cooling electrons in a homogeneous downstream magnetic field (MF) is too soft to produce the low-energy slope of GRB spectra. However, the MF may decay downstream with distance from the shock front. Here we show that the synchrotron spectrum becomes harder if electrons undergo synchrotron and inverse-Compton cooling in a decaying MF. To reconcile this with the typical GRB spectrum with low-energy slope nu F-nu proportional to nu, the postshock MF decay time must be comparable to the cooling time of the bulk electrons (corresponding to a MF decaying length typically of similar to 10(5) skin depths); that the inverse-Compton cooling should dominate synchrotron cooling after the MF decay time; and/or that the MF decays with comoving time roughly as B proportional to t(-1.5). An internal shock synchrotron model with a decaying MF can account for the majority of GRBs with low-energy slopes not harder than nu(4/3).
119203353
The hidden charm decay of Y(4140) by the rescattering mechanism
Abstract Assuming that Y ( 4140 ) is the second radial excitation of the P-wave charmonium χ c J ″ ( J = 0 , 1 ), the hidden charm decay mode of Y ( 4140 ) is calculated in terms of the rescattering mechanism. Our numerical results show that the upper limit of the branching ratio of the hidden charm decay Y ( 4140 ) → J / ψ ϕ is on the order of 10 − 4 – 10 − 3 for both of the charmonium assumptions for Y ( 4140 ) , which disfavors the large hidden charm decay pattern indicated by the CDF experiment. It seems to reveal that the pure second radial excitation of the P-wave charmonium χ c J ″ ( J = 0 , 1 ) is problematic.
55621741
Observation of $e^+e^-\to \chi_{c0}\omega$ and missing higher charmonium $\psi(4S)$
Stimulated by the recent BESIII observation of a new resonance in $e^+ e^- \to \omega \chi_{c0}$ and by the fact that this state is consistent with our predicted $\psi(4S)$, in this work we estimate the meson loop contribution to $\psi(4S) \to \omega \chi_{c0}$. The evaluation indicates that our theoretical estimate can overlap with the experimental data in a reasonable parameter range. This fact shows that introduction of the missing higher charmonium $\psi(4S)$ provides a possible explanation to the recent BESIII observation. The upper limit of a branching ratio of $\psi(4S) \to \eta J/\psi$ is also predicted as $1.9 \times 10^{-3}$, which can be further tested by BESIII, Belle and forthcoming BelleII.
119208539
1-jettiness DIS event shape: NNLL+NLO results
We present results for the complete NNLL+NLO (~ \alpha_s) 1-jettiness (\tau_1) event shape distribution for single jet (J) production in electron-nucleus (N_A) collisions e^- + N_A \to e^- + J + X, in the deep inelastic scattering (DIS) region where the hard scale is set by the jet transverse momentum P_{J_T}. These results cover the entire \tau_1-spectrum including the resummation (\tau_1<<P_{J_T}) and fixed-order (\tau_1~ P_{J_T}) perturbative QCD regions. They incorporate non-perturbative soft radiation effects, the anti-k_T jet algorithm in the fixed-order calculation, and a smooth matching between the resummation and fixed-order perturbative QCD regions. The matching smoothly connects the spectrum in the resummation region, which can be computed without reference to an external jet algorithm, and the fixed-order region where an explicit jet algorithm must be specified. Our code, used for generating the numerical results, is flexible enough to incorporate different jet algorithms for the fixed-order calculation. We also perform a jet shape analysis, defined within the 1-jettiness framework, which allows one to control the amount of radiation included in the definition of the final state jet. This formalism can allow for detailed studies of jet energy-loss mechanisms and nuclear medium effects. The analysis presented here can be used for precision studies of QCD and as a probe of nuclear dynamics using data collected at HERA and in proposed future electron-ion colliders such as the EIC and the LHeC.
116542103
First estimate of producing the charmed baryon $\Lambda_c(2880)$ at PANDA
In the present work we explore the production potential of $\Lambda_c(2880)^+$ at PANDA. With the $J^P=\frac{5}{2}^+$ assignment to $\Lambda_c(2880)^+$, we calculate the differential and total cross sections of $p\bar{p}\to \Lambda_c^-\Lambda_c(2880)^+$. We also perform the Dalitz plot analysis and give the $pD^0$ invariant mass spectrum distribution of the process $p\bar{p}\to \Lambda_c^-pD^0$, where the signal and background contributions are considered. Our numerical results indicate that the production of $\Lambda_c(2880)^+$ may reach up to about 20 $\mu$b. About $10^7$ events from the reconstruction of $pD^0$ can be accumulated per day, if taking the designed luminosity ($2\times10^{32}~\mbox{cm}^{-2}\mbox{s}^{-1}$) of PANDA.
119163459
THE 1-JETTINESS EVENT-SHAPE FOR DIS WITH NNLL RESUMMATION
We propose the use of 1-jettiness, a global event shape, for exclusive single jet production in lepton-nucleus deep inelastic scattering (DIS). We derive a factorization formula, using the Soft-Collinear Effective Theory, differential in the transverse momentum and rapidity of the jet and the 1-jettiness event shape. It provides a quantitative measure of the shape of the final-state QCD radiation in the presence of the hard jet, providing a useful powerful probe of QCD and nuclear physics. For example, one expects differences in the observed pattern of QCD radiation between large and small nuclei and these can be quantified by the 1-jettiness event shape. Numerical results are given for this new DIS event shape at leading twist with resummation at the next-to-next-to-leading logarithmic (NNLL) level of accuracy, for a variety of nuclear targets. Such studies would be ideal at a future EIC or LHeC electron-ion collider, where a range of nuclear targets are planned.