16,331 research outputs found
Photometric catalog of nearby globular clusters (I)
We present the first part of the first large and homogeneous CCD
color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular
clusters (GGC) imaged in the V and I bands using only two telescopes (one for
each hemisphere). The observed clusters represent 75% of the known Galactic
globulars with (m-M)v<=16.15 mag, cover most of the globular cluster
metallicity range (-2.2 <= [Fe/H] <= -0.4), and span Galactocentric distances
from ~1.2 to ~18.5 kpc.
In this paper, the CMDs for the 39 GGCs observed in the southern hemisphere
are presented. The remaining 13 northern hemisphere clusters of the catalog are
presented in a companion paper. For four clusters (NGC 4833, NGC 5986, NGC
6543, and NGC 6638) we present for the first time a CMD from CCD data. The
typical CMD spans from the 22nd V magnitude to the tip of the red giant branch.
Based on a large number of standard stars, the absolute photometric calibration
is reliable to the ~0.02 mag level in both filters.
This catalog, because of its homogeneity, is expected to represent a useful
data base for the measurement of the main absolute and relative parameters
characterizing the CMD of GGCs.Comment: 34 pages, 108 figures, Astronomy & Astrophysics Supplement Series, in
press. Full resolution figures can be obtained from the authors upon reques
Generic Black-Box End-to-End Attack Against State of the Art API Call Based Malware Classifiers
In this paper, we present a black-box attack against API call based machine
learning malware classifiers, focusing on generating adversarial sequences
combining API calls and static features (e.g., printable strings) that will be
misclassified by the classifier without affecting the malware functionality. We
show that this attack is effective against many classifiers due to the
transferability principle between RNN variants, feed forward DNNs, and
traditional machine learning classifiers such as SVM. We also implement GADGET,
a software framework to convert any malware binary to a binary undetected by
malware classifiers, using the proposed attack, without access to the malware
source code.Comment: Accepted as a conference paper at RAID 201
Galactic Globular Cluster Relative Ages
Based on a new large, homogeneous photometric database of 35 Galactic
globular clusters (GGCs), a set of distance and reddening independent relative
age indicators has been measured. The observed D(V-I)_2.5 and D(V)(HB-TO) vs.
metallicity relations have been compared with the relations predicted by two
recent updated libraries of isochrones. Using these models and two independent
methods, we have found that self-consistent relative ages can be estimated for
our GGC sample. Based on the relative age vs. metallicity distribution, we
conclude that: (a) there is no evidence of an age spread for clusters with
[Fe/H]<-1.2, all the clusters of our sample in this range being old and coeval;
(b) for the intermediate metallicity group (-1.2<=[Fe/H]<-0.9) there is a clear
evidence of age dispersion, with clusters up to ~25% younger than the older
members; and (c) the clusters within the metal rich group ([Fe/H]>=-0.9) seem
to be coeval within the uncertainties (except Pal12), but younger (~17%) than
the bulk of the Galactic globulars. The latter result is totally model
dependent. From the distribution of the GGC ages with the Galactocentric
distance, we can present a possible scenario for the Milky Way formation: The
GC formation process started at the same zero age throughout the halo, at least
out to ~20 kpc from the Galactic center. According to the present stellar
evolution models, the metal-rich globulars are formed at a later time (~ 17%
lower age). And finally, significantly younger halo GGCs are found at any
R(GC)>8 kpc. For these, a possible scenario associated with mergers of dwarf
galaxies to the Milky Way is suggested.Comment: 47 pages, 9 figures. To be published in the Astronomical Journal,
November issu
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