94 research outputs found
Testing the universality of star formation - I. Multiplicity in nearby star-forming regions
We have collated multiplicity data for five clusters (Taurus, Chamaeleon I,
Ophiuchus, IC348, and the Orion Nebula Cluster). We have applied the same mass
ratio (flux ratios of delta K <= 2.5) and primary mass cuts (~0.1-3.0 Msun) to
each cluster and therefore have directly comparable binary statistics for all
five clusters in the separation range 62-620 au, and for Taurus, Chamaeleon I,
and Ophiuchus in the range 18-830 au. We find that the trend of decreasing
binary fraction with cluster density is solely due to the high binary fraction
of Taurus, the other clusters show no obvious trend over a factor of nearly 20
in density.
With N-body simulations we attempt to find a set of initial conditions that
are able to reproduce the density, morphology and binary fractions of all five
clusters. Only an initially clumpy (fractal) distribution with an initial total
binary fraction of 73 per cent (17 per cent in the range 62-620 au) is able to
reproduce all of the observations (albeit not very satisfactorily). Therefore,
if star formation is universal the initial conditions must be clumpy and with a
high (but not 100 per cent) binary fraction. This could suggest that most
stars, including M-dwarfs, form in binaries.Comment: Accepted for publication in MNRAS, 19 pages, 22 figure
Testing the universality of star formation - II. Comparing separation distributions of nearby star-forming regions and the field
We have measured the multiplicity fractions and separation distributions of
seven young star-forming regions using a uniform sample of young binaries. Both
the multiplicity fractions and separation distributions are similar in the
different regions. A tentative decline in the multiplicity fraction with
increasing stellar density is apparent, even for binary systems with
separations too close (19-100au) to have been dynamically processed. The
separation distributions in the different regions are statistically
indistinguishable over most separation ranges, and the regions with higher
densities do not exhibit a lower proportion of wide (300-620au) relative to
close (62-300au) binaries as might be expected from the preferential
destruction of wider pairs. Only the closest (19-100au) separation range, which
would be unaffected by dynamical processing, shows a possible difference in
separation distributions between different regions. The combined set of young
binaries, however, shows a distinct difference when compared to field binaries,
with a significant excess of close (19-100au) systems among the younger
binaries. Based on both the similarities and differences between individual
regions, and between all seven young regions and the field, especially over
separation ranges too close to be modified by dynamical processing, we conclude
that multiple star formation is not universal and, by extension, the star
formation process is not universal.Comment: accepted for publication in MNRA
A Photometric Study of the Young Stellar Population Throughout the lambda Orionis Star-Forming Region
We present VRI photometry of 320,917 stars with 11 < R < 18 throughout the
lambda Orionis star-forming region. We statistically remove the field stars and
identify a representative PMS population throughout the interior of the
molecular ring. The spatial distribution of this population shows a
concentration of PMS stars around lambda Ori and in front of the B35 dark
cloud. Few PMS stars are found outside these pockets of high stellar density,
suggesting that star formation was concentrated in an elongated cloud extending
from B35 through lambda Ori to the B30 cloud. We find a lower limit for the
global stellar mass of about 500 Mo. We find that the global ratio of low- to
high-mass stars is similar to that predicted by the field initial mass
function, but this ratio varies strongly as a function of position in the
star-forming region. Locally, the star-formation process does not produce a
universal initial mass function. We construct a history of the star-forming
complex. This history incorporates a recent supernova to explain the
distribution of stars and gas today.Comment: 42 pages, 11 figures; to appear in the Astronomical Journa
Výroba hybridního kompozitu s termoplastickou matricí a aramid-uhlíkovou tkaninou
Příspěvek se zabývá procesem výroby hybridního kompozitu a analýzou vlivu změny postupu
výroby na mechanické vlastnosti. Kompozit byl vyroben z deseti stejně orientovaných vrstev
tkaniny s plátnovou vazbou tvořenou aramidovými vlákny v jednom směru a uhlíkovými
v druhém. Jednotlivé vrstvy tkaniny byly prokládány polyvinyl butyralovou fólií. Následně byly
kompozitní desky vytvrzeny s použitím autoklávu. Výroba byla několikrát opakována a při
jednom opakování byl proces vytvrzování v autoklávu pozměněn. Experimenty provedené na
vzorcích z desek s upraveným postupem výroby a z ostatních desek ukázaly odlišnosti
v mechanických vlastnostech.Tato publikace byla podpořena projektem SGS-2022-008 Ministerstva školství, mládeže
a tělovýchovy ČR
Third Dredge-up in Low Mass Stars: Solving the LMC Carbon Star Mystery
A long standing problem with asymptotic giant branch (AGB) star models has
been their inability to produce the low-luminosity carbon stars in the Large
and Small Magellanic Clouds. Dredge-up must begin earlier and extend deeper. We
find this for the first time in our models of LMC metallicity. Such features
are not found in our models of SMC metallicity. The fully implicit and
simultaneous stellar evolution code STARS has been used to calculate the
evolution of AGB stars with metallicities of Z=0.008 and Z=0.004, corresponding
to the observed metallicities of the Large and Small Magellanic Clouds,
respecitively. Third dredge-up occurs in stars of 1Msol and above and carbon
stars were found for models between 1Msol and 3Msol. We use the detailed models
as input physics for a population synthesis code and generate carbon star
luminosity functions. We now find that we are able to reproduce the carbon star
luminosity function of the LMC without any manipulation of our models. The SMC
carbon star luminosity function still cannot be produced from our detailed
models unless the minimum core mass for third dredge-up is reduced by 0.06Msol.Comment: 6 pages, 5 figures. Accepted for publication in MNRA
WIYN Open Cluster Study. XXXVIII. Stellar Radial Velocities in the Young Open Cluster M35 (NGC 2168)
We present 5201 radial-velocity measurements of 1144 stars, as part of an
ongoing study of the young (150 Myr) open cluster M35 (NGC 2168). We have
observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN
3.5m telescope. Our stellar sample covers main-sequence stars over a magnitude
range of 13.0<V<16.5 (1.6 - 0.8 Msun) and extends spatially to a radius of 30
arcminutes (7 pc in projection at a distance of 805 pc or 4 core radii). Due to
its youth, M35 provides a sample of late-type stars with a range of rotation
periods. Therefore, we analyze the radial-velocity measurement precision as a
function of the projected rotational velocity. For narrow-lined stars (v sin i
< 10 km/s), the radial velocities have a precision of 0.5 km/s, which degrades
to 1.0 km/s for stars with v sin i = 50 km/s. The radial-velocity distribution
shows a well-defined cluster peak with a central velocity of -8.16 +/- 0.05
km/s, permitting a clean separation of the cluster and field stars. For stars
with >=3 measurements, we derive radial-velocity membership probabilities and
identify radial-velocity variables, finding 360 cluster members, 55 of which
show significant radial- velocity variability. Using these cluster members, we
construct a color-magnitude diagram for our stellar sample cleaned of field
star contamination. We also compare the spatial distribution of the single and
binary cluster members, finding no evidence for mass segregation in our stellar
sample. Accounting for measurement precision, we place an upper limit on the
radial-velocity dispersion of the cluster of 0.81 +/- 0.08 km/s. After
correcting for undetected binaries, we derive a true radial-velocity dispersion
of 0.65 +/- 0.10 km/s.Comment: accepted for publication in A
The Effect of Pre-Main Sequence Stars on Star Cluster Dynamics
We investigate the effects of the addition of pre-main sequence evolution to
star cluster simulations. We allowed stars to follow pre-main sequence tracks
that begin at the deuterium burning birthline and end at the zero age main
sequence. We compared our simulations to ones in which the stars began their
lives at the zero age main sequence, and also investigated the effects of
particular choices for initial binary orbital parameters. We find that the
inclusion of the pre-main sequence phase results in a slightly higher core
concentration, lower binary fraction, and fewer hard binary systems. In
general, the global properties of star clusters remain almost unchanged, but
the properties of the binary star population in the cluster can be dramatically
modified by the correct treatment of the pre-main sequence stage.Comment: 40 pages ApJ preprint style Accepted by Ap
WIYN Open Cluster Study. XLVIII. The Hard-Binary Population of NGC 188
(abridged) We present an in-depth study of the hard-binary population of the
old (7 Gyr) open cluster NGC 188. The main-sequence solar-type hard binaries in
NGC 188 are nearly indistinguishable from similar binaries in the Galactic
field. We find a global solar-type main-sequence hard-binary frequency in NGC
188 of 29 +/- 3 % for binaries with periods less than 10^4 days. For
main-sequence hard binaries in the cluster we observe a log-period distribution
that rises towards our detection limit, a roughly Gaussian eccentricity
distribution centered on e = 0.35 (for binaries with periods longer than the
circularization period), and a secondary-mass distribution that rises towards
lower-mass companions. Importantly, the NGC 188 blue straggler binaries show
significantly different characteristics than the solar-type main sequence
binaries in NGC 188. We observe a blue straggler hard-binary frequency of 76
+/- 19 %, three times that of the main sequence. The blue straggler binary
eccentricity - log period distribution is distinct from that of the main
sequence at the 99% confidence level, with the majority of the blue straggler
binaries having periods of order 1000 days and lower eccentricities. The
secondary-mass distribution for these long-period blue straggler binaries is
narrow and peaked with a mean value of about 0.5 Msun. Predictions for
mass-transfer products are most closely consistent with the binary properties
of these NGC 188 blue stragglers, which comprise two-thirds of the blue
straggler population. Additionally we compare the NGC 188 binaries to those
evolved within the sophisticated Hurley et al. (2005) N-body open cluster
simulation. We find that additional simulations with initial conditions that
are better motivated by observations are necessary to properly investigate the
dynamical evolution of a rich binary population in open clusters like NGC 188.Comment: 23 pages, 22 figures, accepted for publication in A
On the Interstellar Medium and Star Formation Demographics of Galaxies in the Local Universe
We present a demographic analysis of integrated star formation and gas
properties for a sample of galaxies representative of the overall population at
z~0. This research was undertaken in order to characterise the nature of star
formation and interstellar medium behaviour in the local universe, and test the
extent to which global star formation rates can be seen as dependent on the
interstellar gas content. Archival 21 cm derived HI data are compiled from the
literature, and are combined with CO (J=1-0) derived H_2 masses to calculate
and characterise the total gas content for a large sample of local galaxies.
The distribution in stellar mass-normalised HI content is found to exhibit the
noted characteristic transition at stellar masses of ~3x10^10 M_sun, turning
off towards low values, but no such transition is observed in the equivalent
distribution of molecular gas. H-alpha based star formation rates and specific
star formation rates are also compiled for a large (1110) sample of local
galaxies. We confirm two transitions as found in previous work: a turnover
towards low SFRs at high luminosities, indicative of the quenching of SF
characteristic of the red sequence; and a broadening of the SF distribution in
low-luminosity dwarf galaxies, again to extremely low SFRs of < 0.001 M_sun/yr.
However, a new finding is that while the upper luminosity transition is
mirrored by the turn over in HI content, suggesting that the low SFRs of the
red sequence result from a lack of available gas supply, the transition towards
a large spread of SFRs in the least luminous dwarf galaxies is not matched by a
prominent increase in scatter in gas content. Possible mass-dependent quenching
mechanisms are discussed, along with speculations that in low mass galaxies,
the H-alpha luminosity may not faithfully trace the SFR.Comment: 15 pages, 12 figures; accepted for publication in MNRA
The Stellar Populations of M33's Outer Regions IV: Inflow History and Chemical Evolution
We have modelled the observed color-magnitude diagram (CMD) at one location
in M33's outskirts under the framework of a simple chemical evolution scenario
which adopts instantaneous and delayed recycling for the nucleosynthetic
products of Type II and Ia supernovae. In this scenario, interstellar gas forms
stars at a rate modulated by the Kennicutt-Schmidt relation and gas outflow
occurs at a rate proportional to the star formation rate (SFR). With this
approach, we put broad constraints on the role of gas flows during this
region's evolution and compare its [alpha/Fe] vs. [Fe/H] relation with that of
other Local Group systems. We find that models with gas inflow are
significantly better than the closed box model at reproducing the observed
distribution of stars in the CMD. The best models have a majority of gas inflow
taking place in the last 7 Gyr, and relatively little in the last 3 Gyr. These
models predict most stars in this region to have [alpha/Fe] ratios lower than
the bulk of the Milky Way's halo. The predictions for the present-day SFR, gas
mass, and oxygen abundance compare favorably to independent empirical
estimates. Our results paint a picture in which M33's outer disc formed from
the protracted inflow of gas over several Gyr with at least half of the total
inflow occurring since z ~ 1.Comment: 22 pages, 12 figures, accepted to MNRA
- …