2,468 research outputs found
Computing Matveev's complexity via crystallization theory: the boundary case
The notion of Gem-Matveev complexity has been introduced within
crystallization theory, as a combinatorial method to estimate Matveev's
complexity of closed 3-manifolds; it yielded upper bounds for interesting
classes of such manifolds. In this paper we extend the definition to the case
of non-empty boundary and prove that for each compact irreducible and
boundary-irreducible 3-manifold it coincides with the modified Heegaard
complexity introduced by Cattabriga, Mulazzani and Vesnin. Moreover, via
Gem-Matveev complexity, we obtain an estimation of Matveev's complexity for all
Seifert 3-manifolds with base and two exceptional fibers and,
therefore, for all torus knot complements.Comment: 27 pages, 14 figure
High Resolution Near-Infrared Spectra of Protostars
We present new high resolution (R = 21,000) near-infrared (2 microns)
spectroscopic observations of a sample of Class I and flat-spectrum
protostellar objects in the rho Ophiuchi dark cloud. None of the five Class I
spectra show CO v = 0 -- 2 absorption features, consistent with high K-band
continuum veilings, 4 <= r_k <= 20 and fast stellar rotation, assuming that the
underlying protostellar photospheres are of late spectral type, as is suggested
by the low luminosities of most of these objects. Two of the flat-spectrum
protostellar objects also show no absorption features and are likely to be
highly veiled. The remaining two flat-spectrum sources show weak, broad
absorptions which are consistent with an origin in quickly rotating (v sin i ~
50 km / s) late-type stellar photospheres which are also strongly veiled, r_k =
3 - 4. These observations provide further evidence that: 1)-Class I sources are
highly veiled at near-infrared wavelengths, confirming previous findings of
lower resolution spectroscopic studies; and 2)- flat-spectrum protostars rotate
more rapidly than classical T Tauri stars (Class II sources), supporting
findings from a recent high resolution spectroscopic study of other
flat-spectrum sources in this cloud. In addition our observations are
consistent with the high rotation rates derived for two of the Class I
protostellar objects in our sample from observations of variable hard X-ray
emission obtained with the ASCA satellite. These observations suggest that
certain Class I sources can rotate even more rapidly than flat-spectrum
protostars, near breakup velocity.Comment: 16 pages including 2 tables and 2 figures (AASTeX 5.x) to be
published in The Astronomical Journal July 200
Uncovering Spiral Structure in Flocculent Galaxies
We present K'(2.1 micron) observations of four nearby flocculent spirals,
which clearly show low-level spiral structure and suggest that kiloparsec-scale
spiral structure is more prevalent in flocculent spirals than previously
supposed. In particular, the prototypical flocculent spiral NGC 5055 is shown
to have regular, two-arm spiral structure to a radius of 4 kpc in the near
infrared, with an arm-interarm contrast of 1.3. The spiral structure in all
four galaxies is weaker than that in grand design galaxies. Taken in unbarred
galaxies with no large, nearby companions, these data are consistent with the
modal theory of spiral density waves, which maintains that density waves are
intrinsic to the disk. As an alternative, mechanisms for driving spiral
structure with non-axisymmetric perturbers are also discussed. These
observations highlight the importance of near infrared imaging for exploring
the range of physical environments in which large-scale dynamical processes,
such as density waves, are important.Comment: 12 pages AASTeX; 3 compressed PS figures can be retrieved from
ftp://ftp.astro.umd.edu/pub/michele as file thornley.tar (1.6Mbytes).
Accepted to Ap.J. Letters.(Figures now also available here, and from
ftp://ftp.astro.umd.edu/pub/michele , in GIF format.
Low-Mass Star Formation and the Initial Mass Function in the Rho Ophiuchi Cloud Core
We have obtained moderate-resolution (R=800-1200) K-band spectra for ~100
stars within and surrounding the cloud core of rho Oph. We have measured
spectral types and continuum veilings and have combined this information with
results from new deep imaging. The IMF peaks at about 0.4 M_sun and slowly
declines to the hydrogen burning limit with a slope of ~-0.5 in logarithmic
units (Salpeter is +1.35). Our lower limits on the numbers of substellar
objects demonstrate that the IMF probably does not fall more steeply below the
hydrogen burning limit, at least down to ~0.02 M_sun. We then make the first
comparison of mass functions of stars and pre-stellar clumps (Motte, Andre, &
Neri) measured in the same region. The similar behavior of the two mass
functions in rho Oph supports the suggestion of Motte et al. and Testi &
Sargent that the stellar mass function in young clusters is a direct product of
the process of cloud fragmentation. After considering the effect of extinction
on the SED classifications of the sample, we find that ~17% of the rho Oph
stars are Class I, implying ~0.1 Myr for the lifetime of this stage. In spectra
separated by two years, we observe simultaneous variability in the Br gamma
emission and K-band continuum veiling for two stars, where the hydrogen
emission is brighter in the more heavily veiled data. This behavior indicates
that the disk may contribute significantly to continuous K-band emission, in
contrast to the proposal that the infalling envelope always dominates. Our
detection of strong 2 micron veiling (r_K=1-4) in several Class II and III
stars, which should have disks but little envelope material, further supports
this proposition.Comment: 35 pages, 14 figures, accepted to Ap
A Companion Galaxy to the Post-Starburst Quasar UN J1025-0040
UN J1025-0040 is a quasar at z = 0.6344 that shows an extremely bright post
starburst population of age ~ 400 Myr (Brotherton et al. 1999). Images of UN
J1025-0040 show a nearly stellar object 4.2 arcseconds SSW of the quasar. We
present imaging and spectroscopy that confirm that this object is a companion
galaxy at redshift z = 0.6341. We estimate an age of ~ 800 Myr for the dominant
stellar population in the companion. The companion appears to be interacting
with the quasar host galaxy, and this interaction may have triggered both the
starburst and the quasar activity in UN J1025-0040.Comment: 8 pages plus 4 figures (2 postscript, 2 jpg). Postscript version
available at http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
the January 2000 issue of A
A Contracting, Turbulent, Starless Core in the Serpens Cluster
We present combined single-dish and interferometric CS(2--1) and N2H+(1--0)
observations of a compact core in the NW region of the Serpens molecular cloud.
The core is starless according to observations from optical to millimeter
wavelengths and its lines have turbulent widths and ``infall asymmetry''. Line
profile modeling indicates supersonic inward motions v_in>0.34 km/s over an
extended region L>12000AU. The high infall speed and large extent exceeds the
predictions of most thermal ambipolar diffusion models and points to a more
dynamical process for core formation. A short (dynamic) timescale, ~1e5
yr=L/v_in, is also suggested by the low N2H+ abundance ~1e-10.Comment: 11 pages including 2 figures. Accepted for publication in the
Astrophysical Journal Letter
High Angular Resolution JHK Imaging of the Centers of the Metal-Poor Globular Clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341 (M92)
The Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) has
been used to obtain high angular resolution JHK images of the centers of the
metal-poor globular clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341
(M92). The color-magnitude diagrams (CMDs) derived from these data include the
upper main sequence and most of the red giant branch (RGB), and the cluster
sequences agree with published photometric measurements of bright stars in
these clusters. The photometric accuracy is limited by PSF variations, which
introduce systematic errors of a few hundredths of a magnitude near the AO
reference star.
The clusters are paired according to metallicity, and the near-infrared CMDs
and luminosity functions are used to investigate the relative ages within each
pair. The near-infrared CMDs provide the tightest constraints on the relative
ages of the classical second parameter pair NGC5272 and NGC6205, and indicate
that these clusters have ages that differ by no more than +/- 1 Gyr. These
results thus support the notion that age is not the second parameter. We
tentatively conclude that NGC6287 and NGC6341 have ages that differ by no more
than +/- 2 Gyr. However, the near-infrared spectral energy distributions of
stars in NGC6287 appear to differ from those of stars in outer halo clusters,
bringing into question the validity of this age estimate.Comment: 22 pages, 17 figures. To be published in the Astronomical Journa
VLA 3.5 cm continuum sources in the Serpens cloud core
We present VLA 3.5 cm continuum observations of the Serpens cloud core. 22
radio continuum sources are detected. 16 out of the 22 cm sources are suggested
to be associated with young stellar objects (Class 0, Class I, flat-spectrum,
and Class II) of the young Serpens cluster. The rest of the VLA sources
plausibly are background objects. Most of the Serpens cm sources likely
represent thermal radio jets; on the other hand, the radio continuum emission
of some sources could be due to a gyrosynchroton mechanism arising from
coronally active young stars. The Serpens VLA sources are spatially distributed
into two groups; one of them located towards the NW clump of the Serpens core,
where only Class 0 and Class I protostars are found to present cm emission, and
a second group located towards the SE clump, where radio continuum sources are
associated with objects in evolutionary classes from Class 0 to Class II. This
subgrouping is similar to that found in the near IR, mid-IR and mm wavelength
regimes.Comment: 2 figures, accepted by Astronomical journa
Recommended from our members
High resolution molecular line observations of the Serpens Nebula
The Serpens Molecular cloud is a nearby low/intermediate mass star forming region that is in the final stages of forming a densely packed cluster of stars. Spectra and high angular resolution maps of the CO, 13CO, C18O and C17O J=2-1 and CO J=4-3 transitions were obtained to study the distribution of molecular gas near the cluster. These are supplemented with data on the J=4-3 HCO+ line (to probe the denser gas), and 3P1 - 3P0 line of atomic carbon. The mass of the region is estimated to be ~1450Msun, implying that the star formation efficiency in the region to date has been ~2.5percent. Several molecular outflows are visible in the maps; some are associated with compact objects visible in millimetre and submillimetre wave continuum maps, as well as more widespread diffuse high velocity gas that extends over much of the nebula. The mass and energy of material in the high velocity gas are relatively small, ~0.3Msun and 3 x 1045 erg s-1, consistent with the characteristics of outflows seen towards low mass star-formation regions. The directions of the overlapping outflow lobes do not however show a clear alignment with the cloud's large scale magnetic field as has been reported towards some other regions. The gas temperatures in the central part of the molecular cloud are warmer (~30-40K) than typical for dark clouds, suggesting that the Serpens cluster has interacted with, and heated this gas. Estimates of the CO isotopomeric abundance ratios from these data may be strongly affected by opacity and radiative transfer effects. In a comparison of the LTE and LVG techniques, the disagreement between the derived column densities is discussed - with particular relevance to the higher rotationa
- …