arXiv subjects

Jin Zhu

Publications and source records attributed to Jin Zhu.

66 records · Page 4Linked to original sources

arXiv2005

B_s \to ρ(ω) K^* with Perturbative QCD approach

$B_s \to ρ(ω) K^{\ast}$ are useful to determine the $B_s$ distribution amplitude, as well as constrain the CKM phase angle $α$. We study these decays within the Perturbative QCD (PQCD) picture. In this approach, we calculate factorizable, non-factorizable, as well as annihilation diagrams. We find the branching ratio for $B_s \to ρ^+ K^{*-}$ is big to order $10^{-5}$, we also find there's large direct CP violation in $B_s(\bar B_s) \to ρ^0(ω) \bar K^{*0}(K^{*0})$. Our predictions are consistent with those from other methods and current experiments.

hep-ph↗

arXiv2005

$B^0 \to ϕϕ$ Decay in Perturbative QCD Approach

The rare decay $B^0 \to ϕϕ$ can occur only via penguin annihilation topology in the standard model. We calculate this channel in the perturbative QCD approach. The predicted branching ratio is very small at ($10^{-8}$). We also give the polarization fractions, which shows that the transverse polarization contribution is comparable to the longitudinal one, due to a big transverse contribution from factorizable diagrams. The small branching ratio in SM, makes it sensitive to any new physics contributions.

hep-ph↗

arXiv2005

Polarization, CP Asymmetry and Branching ratios in B \to K^* K^* with Perturbative QCD approach

We study the charmless rare decays $B \to K^{\ast} K^{\ast}$ within the Perturbative QCD picture. We calculate not only factorizable and non-factorizable diagrams, but also annihilation ones. Our predictions are the following: The longitudinal polarization fraction vary from 75% to 99% depending on channels, the branching ratios are of order $10^{-7}$ for $B^0(\bar{B}^0) \to K^{\ast0}\bar{K}^{\ast0}$ and $B^{\pm} \to K^{\ast\pm} \bar{K}^{\ast0}(K^{\ast0})$, much bigger than that for $B^0(\bar{B}^0) \to K^{\ast+}K^{\ast-}$($10^{-8}$). The direct CP asymmetry in $B^{\pm} \to K^{\ast\pm} \bar{K}^{\ast0}(K^{\ast0})$ and $B^0(\bar{B}^0) \to K^{\ast+}K^{\ast-}$ is about -15% and -65% if we choose $α(ϕ_2)$ as $95^{\circ}$. There's no direct CPV in $B^0(\bar{B}^0) \to K^{\ast0}\bar{K}^{\ast0}$ decays because of the pure $b \to d$ penguin topology. Our predictions will be tested in the future B experiments.

hep-ph↗

arXiv2002

Spectral Energy and Age Distributions for 51 Globular Cluster Candidates

This paper is the fourth in a series presenting spectrophotometry of 51 globular cluster candidates, that were detected by Mochejska et al. in the nearby galaxy M33 using the data collected by the DIRECT project. The frames of M33 in this study were taken as part of the BATC Multicolor Sky Survey. We obtained the spectral energy distributions of these candidates in 13 intermediate-band filters. By comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual & Charlot, we estimated their ages. The BC96 models provide the evolution in time of the spectrophotometric properties of simple stellar populations for a wide range of stellar metallicity. Our results show that half of the candidates are younger than 10^8 years, whose age degeneracy is not pronounced. We also find that globular clusters formed continuously in M33 from ~4*10^6 -- 10^{10} years. Our results are in agreement with Chandar et al., who estimated ages for 35 globular clusters candidates in common by comparing the photometric measurements to integrated colors from theoretical models by Bertelli et al. The Kolmogorov-Smirnov Test shows that the maximum value of the absolute difference of estimated ages between Chandar et al. and us is 0.48, and the significance level probability is 100.00 per cent.

astro-ph↗

arXiv2002

15 colour photometry of Landolt SA95 standard star field

In this paper, we present a set of photometric observations in 15 colors of stars in the Landolt covered by the system range from 300 nm to 1000 nm. Visual magnitudes of the stars being studied in the field are from 10th to 20th mag. The observational methodology and the data reduction procedures are described. The relationships between the BATC intermediate-band system and the Landolt UBVRI broad band system are obtained. A catalogue of the photometry has been produced which contains the SEDs of 3613 stars. The electronic form of this catalogue can be accessed at the CDS via anonymous ftp to cdsarc.u-strasbg.fr.

astro-ph↗

arXiv2002

Multicolor photometry of 145 of the HII regions in M33

This paper is the first in a series presenting CCD multicolor photometry for 145 HII regions, selected from 369 candidate regions from Boulesteix et al. (1974), in the nearby spiral galaxy M33. The observations, which covered the whole area of M33, were carried out by the Beijing Astronomical Observatory 60/90 cm Schmidt Telescope, in 13 intermediate-band filters, covering a range of wavelength from 3800 to 10000 A. This provides a series of maps which can be converted to a multicolor map of M33, in pixels of 1.7''*1.7''. Using aperture photometry we obtain the spectral energy distributions (SEDs) for these HII regions. We also give their identification charts. Using the relationship between the BATC intermediate-band system used for the observations and the UBVRI broad-band system, the magnitudes in the B and V bands are then derived. Histograms of the magnitudes in V and in B-V are plotted, and the color-magnitude diagram is also given. The distribution of magnitudes in the V band shows that the apparent magnitude of almost all the regions is brighter than 18, corresponding to an absolute magnitude of -6.62 for an assumed distance modulus of 24.62, which corresponds to a single main sequence O5 star, while the distribution of color shows that the sample is blue, with a mode close to -0.05 as would be expected from a range of typical young clusters.

astro-ph↗

arXiv2002

Spectral Energy Distributions and Age Estimates of 78 Star Clusters in M33

In this third paper of our series, we present CCD spectrophotometry of 78 star clusters that were detected by Chandar, Bianchi, & Ford in the nearby spiral galaxy M33. CCD images of M33 were obtained as a part of the BATC Color Survey of the sky in 13 intermediate-band filters from 3800 to 10000Å. By aperture photometry, we obtain the spectral energy distributions of these 78 star clusters. As Chandar, Bianchi, & Ford did, we estimate the ages of our sample clusters by comparing the photometry of each object with theoretical stellar population synthesis models for different values of metallicity. We find that the sample clusters formed continuously in M33 from $\sim 3\times10^6$ -- $10^{10}$ years. This conclusion is consistent with Chandar, Bianchi, & Ford. The results also show that, there are two peaks in cluster formation, at $\sim 8\times10^6$ and $\sim 10^9$ years in these clusters.

astro-ph↗

arXiv2002

SED, Metallicity and Age of Halo Globular Clusters in M33

In this paper we study the properties of ten halo globular clusters in the nearby spiral galaxy M33. CCD images of M33 were obtained as a part of the BATC Colour Survey of the sky in 13 intermediate-band filters from 3800 to 10000Å. By aperture photometry, we obtain the spectral energy distributions (SEDs) of these globular clusters. We estimate the ages of our sample clusters by comparing the photometry of each object with theoretical stellar population synthesis models for different values of metallicity. Our results suggest that eight of the ten sample halo globular clusters have ``intermediate'' ages, i.e. between 1 and 8 Gyrs.

astro-ph↗

arXiv2002

Multicolor photometry of the galaxies in the central region of Abell 2634

An optical photometric observation with the BATC multicolor system is carried out for the central 56' x 56' region of the nearby cluster of galaxies, Abell 2634. We achieved the spectral energy distributions (SEDs) of 5572 sources detected down to $V \sim 20$ mag, including 178 previously known galaxies, with fourteen filters covering a wavelength range from 3600 Å to 10000 Å. After excluding the foreground and background galaxies, a sample of 124 known members is formed for an investigation of the SED properties. Based on the knowledge of SED properties of member galaxies, we performed the selection of faint galaxies belonging to Abell 2634. The color-color diagrams are powerful in the star/galaxy separation, and 359 faint galaxies are selected by their color features. The technique of photometric redshift and color-magnitude correlation for the early-type galaxies are applied for these faint galaxies, and a list of 74 faint member galaxies is achieved. Basis on the enlarged sample of member galaxies, the spatial distribution and color-magnitude relation of the galaxies in core region of Abell 2634 are discussed. We find a tendency that the color index dispersion of the early-type members is larger for the outer region, which might reflect some clues about the environmental effect on the evolution of galaxies in a cluster.

astro-ph↗

arXiv2001

SED, Age and Metallicity of Star Clusters in M33

In this paper we present CCD spectrophotometry of the star clusters that were detected by Chandar, Bianchi, & Ford in the nearby spiral galaxy M33, using the images obtained with the Beijing Astronomical Observatory 60/90 cm Schmidt Telescope in 13 intermediate-band filters from 3800 to 10000Å. The observations cover the whole area of M33 with a total integration of 32.75 hours from September 23, 1995 to August 28, 2000. This provides a multi-color map of M33 in pixels of $1.7'' \times 1.7''$. By aperture photometry, we obtain the spetral energy distributions (SEDs) of these star clusters. Using theoretical stellar population synthesis models, we also obtain the distributions of age and metallicity of of these star clusters. These clusters formed continuously from $\sim 3\times10^6$ -- $10^{10}$ years, and have a large span of metallicity from ${\rm {Z}=0.0004}$ to ${\rm {Z}=0.05}$.

astro-ph↗

arXiv1998

Ring structure and warp of NGC5907 -- Interaction with dwarf galaxies

The edge-on, nearby spiral galaxy NGC5907 has long been used as the prototype of a ``non-interacting'' warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC5907 close to one of the ring's foci. This suggests the ring material is in orbit around NGC5907. No gaseous component to the ring has been detected either with deep H$α$ images or in Very Large Array (VLA) HI 21-cm line maps. The visible material in the ring has an integrated luminosity <= 10^8 L_sun and its brightest part has a color R-I ~ 0.9. All of these properties are consistent with the ring being a tidally-disrupted dwarf spheroidal galaxy. Second, we find that NGC5907 has a dwarf companion galaxy, PGC54419, projected to be only 36.9 kpc from the center of NGC5907, close in radial velocity (ΔV = 45 km s^{-1}) to the giant spiral galaxy. This dwarf is seen at the tip of the HI warp and in the direction of the warp. Hence, NGC5907 can no longer be considered ``non-interacting,'' but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies.

astro-ph↗

arXiv1996

Deep Wide-Field Spectrophotometry of the Open Cluster M67

We present nine color CCD intermediate-band spectrophotometry of a two square degree field centered on the old open cluster M67, from 3890$\rm Å$ to nearly 1$μ$. These observations are taken as a part of the BATC (Beijing-Arizona-Taipei-Connecticut) Color Survey of the Sky, for both scientific and calibration reasons. With these data we show that the BATC survey can reach its goal of obtaining spectrophotometry to a zero point accuracy of 0.01 mag, and down to V = 21 with 0.3 mag random error. We fit the color-magnitude diagrams (CMDs) with Worthey's theoretical models. The net result is the excellent fit of the 4.0 Gyr, [Fe/H] = $-0.10$ model to our data, including a good fit to the main sequence (MS) turn-off. Our data are consistent with a toy model with 50\% of the stars in M67 being binaries and a random distribution of binary mass-ratios, although other models with different mass-ratio distributions cannot be ruled out. The spatial distribution and mass function (MF) of stars in M67 show marked effects of dynamical evolution and evaporation of stars from the cluster. Blue stragglers and binary stars are the most condensed within the cluster, with degree of condensation depending on mass.We find M67 to have an elongated shape, oriented at an angle of $15^{\circ}$ relative to the galactic plane. Within its tidal radius, the observed MF of M67 between 1.2 $\rm M_\odot$ and $\rm 0.8 M_\odot$ has a Salpeter slope $\rm η= -1.93 \pm 0.66$. For stars of mass below 0.8 $\rm M_\odot$, $\rm η\sim 0$. It is plausible that the leveling-off of the MF at lower masses is a result of evaporation of lower mass stars in this mass range at a rate of one every $\sim 10^7$ years. If so, it is plausible that the IMF of M67 has the canonical field value of $\rm η= -2.0$.

astro-ph↗