189 research outputs found
The binary companion mass ratio distribution: an imprint of the star formation process?
We explore the effects of dynamical evolution in dense clusters on the
companion mass ratio distribution (CMRD) of binary stars. Binary systems are
destroyed by interactions with other stars in the cluster, lowering the total
binary fraction and significantly altering the initial semi-major axis
distribution. However, the shape of the CMRD is unaffected by dynamics; an
equal number of systems with high mass ratios are destroyed compared to systems
with low mass ratios. We might expect a weak dependence of the survivability of
a binary on its mass ratio because its binding energy is proportional to both
the primary and secondary mass components of the system. However, binaries are
broken up by interactions in which the perturbing star has a significantly
higher energy (by a factor of >10, depending on the particular binary
properties) than the binding energy of the binary, or through multiple
interactions in the cluster. We therefore suggest that the shape of the
observed binary CMRD is an outcome of the star formation process, and should be
measured in preference to the distributions of orbital parameters, such as the
semi-major axis distribution.Comment: 8 pages, 4 figures, accepted for publication in MNRA
Imaging the Inner and Outer Gaps of the Pre-Transitional Disk of HD 169142 at 7 mm
We present Very Large Array observations at 7 mm that trace the thermal
emission of large dust grains in the HD 169142 protoplanetary disk. Our images
show a ring of enhanced emission of radius ~25-30 AU, whose inner region is
devoid of detectable 7 mm emission. We interpret this ring as tracing the rim
of an inner cavity or gap, possibly created by a planet or a substellar
companion. The ring appears asymmetric, with the western part significantly
brighter than the eastern one. This azimuthal asymmetry is reminiscent of the
lopsided structures that are expected to be produced as a consequence of
trapping of large dust grains. Our observations also reveal an outer annular
gap at radii from ~40 to ~70 AU. Unlike other sources, the radii of the inner
cavity, the ring, and the outer gap observed in the 7 mm images, which trace
preferentially the distribution of large (mm/cm sized) dust grains, coincide
with those obtained from a previous near-infrared polarimetric image, which
traces scattered light from small (micron- sized) dust grains. We model the
broad-band spectral energy distribution and the 7 mm images to constrain the
disk physical structure. From this modeling we infer the presence of a small
(radius ~0.6 AU) residual disk inside the central cavity, indicating that the
HD 169142 disk is a pre-transitional disk. The distribution of dust in three
annuli with gaps in between them suggests that the disk in HD 169142 is being
disrupted by at least two planets or substellar objects.Comment: Accepted by ApJ Letters, 16 pages, 3 figures, ApJ Letters 201
Discovery of a Companion Candidate in the HD169142 Transition Disk and the Possibility of Multiple Planet Formation
We present L' and J-band high-contrast observations of HD169142, obtained
with the VLT/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager,
respectively. A source located at 0".156+/-0".032 north of the host star
(PA=7.4+/-11.3 degrees) appears in the final reduced L' image. At the distance
of the star (~145 pc), this angular separation corresponds to a physical
separation of 22.7+/-4.7 AU, locating the source within the recently resolved
inner cavity of the transition disk. The source has a brightness of
L'=12.2+/-0.5 mag, whereas it is not detected in the J band (J>13.8 mag). If
its L' brightness arose solely from the photosphere of a companion and given
the J-L' color constraints, it would correspond to a 28-32 MJupiter object at
the age of the star, according to the COND models. Ongoing accretion activity
of the star suggests, however, that gas is left in the inner disk cavity from
which the companion could also be accreting. In this case the object could be
lower in mass and its luminosity enhanced by the accretion process and by a
circumplanetary disk. A lower mass object is more consistent with the observed
cavity width. Finally, the observations enable us to place an upper limit on
the L'-band flux of a second companion candidate orbiting in the disk annular
gap at ~50 AU, as suggested by millimeter observations. If the second companion
is also confirmed, HD169142 might be forming a planetary system, with at least
two companions opening gaps and possibly interacting with each other.Comment: Accepted to ApJL, see also Biller et al. 201
Binary Formation Mechanisms: Constraints from the Companion Mass Ratio Distribution
We present a statistical comparison of the mass ratio distribution of
companions, as observed in different multiplicity surveys, to the most recent
estimate of the single object mass function (Bochanski et al. 2010). The main
goal of our analysis is to test whether or not the observed companion mass
ratio distribution (CMRD) as a function of primary star mass and star formation
environment is consistent with having been drawn from the field star IMF. We
consider samples of companions for M dwarfs, solar type and intermediate mass
stars, both in the field as well as clusters or associations, and compare them
with populations of binaries generated by random pairing from the assumed IMF
for a fixed primary mass. With regard to the field we can reject the hypothesis
that the CMRD was drawn from the IMF for different primary mass ranges: the
observed CMRDs show a larger number of equal-mass systems than predicted by the
IMF. This is in agreement with fragmentation theories of binary formation. For
the open clusters {\alpha} Persei and the Pleiades we also reject the IMF
random- pairing hypothesis. Concerning young star-forming regions, currently we
can rule out a connection between the CMRD and the field IMF in Taurus but not
in Chamaeleon I. Larger and different samples are needed to better constrain
the result as a function of the environment. We also consider other companion
mass functions (CMF) and we compare them with observations. Moreover the CMRD
both in the field and clusters or associations appears to be independent of
separation in the range covered by the observations. Combining therefore the
CMRDs of M and G primaries in the field and intermediate mass primary binaries
in Sco OB2 for mass ratios, q = M2/M1, from 0.2 to 1, we find that the best
chi-square fit follows a power law dN/dq \propto q^{\beta}, with {\beta} =
-0.50 \pm 0.29, consistent with previous results.Comment: 9 pages, 9 figures, Accepted for publication in The Astrophysical
Journa
Distribution of HbS Allele and Haplotypes in a Multi-Ethnic Population of Guinea Bissau, West Africa: Implications for Public Health Screening
BACKGROUND: Sickle Cell Disease (SCD) is an inherited condition that is widespread globally and especially in malaria-endemic West African countries. Limited epidemiological data on SCD are available for Guinea Bissau, where newborn screening is not yet implemented, routine diagnosis is not available, and care is case directed. METHODS: Dried blood spots were collected from children accessing two hospitals managed by Italian Non-Governmental Organizations in the capital city of Bissau and sent to Padova for Hemoglobin (Hb) quantification through HPLC and molecular analysis. Beta globin gene analysis was performed in all; and Hb haplotype of the HbSS and HbSA patients was performed in South Africa. One hundred samples belonging to the most frequent ethnic groups were randomly selected for detection of G6PD mutations. RESULTS: Samples from 848 consecutive children (498 males and 350 females, mean age 6.8 years) accessing the two hospitals were analyzed: 6.95% AS (4.42% allelic frequency), 0.94% SS, and 0.23% AC. 376G G6PD allelic frequency was 24%; 14.8% in AS individuals. The Senegal haplotype was the most prevalent (31%), and the proposition of chromosomes with the atypical haplotype was surprisingly high (56%). CONCLUSION: Our study demonstrates a significant frequency of the HbS allele in the population of Guinea Bissau supporting the implementation of screening strategies. The differences among ethnic groups can help guide targeted interventions for SCD awareness campaigns and determine priority areas for public health interventions. The pilot analysis on haplotypes reveals a large proportion of the atypical haplotype, which may be indicative of a genetically heterogeneous population
Three years of harvest with the vector vortex coronagraph in the thermal infrared
For several years, we have been developing vortex phase masks based on
sub-wavelength gratings, known as Annular Groove Phase Masks. Etched onto
diamond substrates, these AGPMs are currently designed to be used in the
thermal infrared (ranging from 3 to 13 {\mu}m). Our AGPMs were first installed
on VLT/NACO and VLT/VISIR in 2012, followed by LBT/LMIRCam in 2013 and
Keck/NIRC2 in 2015. In this paper, we review the development, commissioning,
on-sky performance, and early scientific results of these new coronagraphic
modes and report on the lessons learned. We conclude with perspectives for
future developments and applications.Comment: To appear in SPIE proceedings vol. 990
Differences in cardiac phenotype and natural history of laminopathies with and without neuromuscular onset
Objective: To investigate differences in cardiac manifestations of patients affected by laminopathy, according to the presence or absence of neuromuscular involvement at presentation.Methods: We prospectively analyzed 40 consecutive patients with a diagnosis of laminopathy followed at a single centre between 1998 and 2017. Additionally, reports of clinical evaluations and tests prior to referral at our centre were retrospectively evaluated.Results: Clinical onset was cardiac in 26 cases and neuromuscular in 14. Patients with neuromuscular presentation experienced first symptoms earlier in life (11 vs 39 years; p < 0.0001) and developed atrial fibrillation/flutter (AF) and required pacemaker implantation at a younger age (28 vs 41 years [p = 0.013] and 30 vs 44 years [p = 0.086] respectively), despite a similar overall prevalence of AF (57% vs 65%; p = 0.735) and atrio-ventricular (A-V) block (50% vs 65%; p = 0.500). Those with a neuromuscular presentation developed a cardiomyopathy less frequently (43% vs 73%; p = 0.089) and had a lower rate of sustained ventricular tachyarrhythmias (7% vs 23%; p = 0.387). In patients with neuromuscular onset rhythm disturbances occurred usually before evidence of cardiomyopathy. Despite these differences, the need for heart transplantation and median age at intervention were similar in the two groups (29% vs 23% [p = 0.717] and 43 vs 46 years [p = 0.593] respectively).Conclusions: In patients with laminopathy, the type of disease onset was a marker for a different natural history. Specifically, patients with neuromuscular presentation had an earlier cardiac involvement, characterized by a linear and progressive evolution from rhythm disorders (AF and/or A-V block) to cardiomyopathy
Discovery of a directly imaged planet to the young solar analog YSES 2
Context. To understand the origin and formation pathway of wide-orbit gas giant planets, it is necessary to expand the limited sample of these objects. The mass of exoplanets derived with spectrophotometry, however, varies strongly as a function of the age of the system and the mass of the primary star.
Aims. By selecting stars with similar ages and masses, the Young Suns Exoplanet Survey (YSES) aims to detect and characterize planetary-mass companions to solar-type host stars in the Scorpius-Centaurus association.
Methods. Our survey is carried out with VLT/SPHERE with short exposure sequences on the order of 5 min per star per filter. The subtraction of the stellar point spread function (PSF) is based on reference star differential imaging using the other targets (with similar colors and magnitudes) in the survey in combination with principal component analysis. Two astrometric epochs that are separated by more than one year are used to confirm co-moving companions by proper motion analysis.
Results. We report the discovery of YSES 2b, a co-moving, planetary-mass companion to the K1 star YSES 2 (TYC 8984-2245-1, 2MASS J11275535-6626046). The primary has a Gaia EDR3 distance of 110 pc, and we derive a revised mass of 1.1 M_⊙ and an age of approximately 14 Myr. We detect the companion in two observing epochs southwest of the star at a position angle of 205° and with a separation of ~1."05, which translates to a minimum physical separation of 115 au at the distance of the system. Photometric measurements in the H and K_s bands are indicative of a late L spectral type, similar to the innermost planets around HR 8799. We derive a photometric planet mass of 6.3_(−0.9)^(+1.6) M_(Jup) using AMES-COND and AMES-dusty evolutionary models; this mass corresponds to a mass ratio of q = (0.5 ± 0.1)% with the primary. This is the lowest mass ratio of a direct imaging planet around a solar-type star to date. We discuss potential formation mechanisms and find that the current position of the planet is compatible with formation by disk gravitational instability, but its mass is lower than expected from numerical simulations. Formation via core accretion must have occurred closer to the star, yet we do not find evidence that supports the required outward migration, such as via scattering off another undiscovered companion in the system. We can exclude additional companions with masses greater than 13 M_(Jup) in the full field of view of the detector (0."152" we are sensitive to planets with masses as low as 2 M_(Jup).
Conclusions. YSES 2b is an ideal target for follow-up observations to further the understanding of the physical and chemical formation mechanisms of wide-orbit Jovian planets. The YSES strategy of short snapshot observations (≤5 min) and PSF subtraction based on a large reference library proves to be extremely efficient and should be considered for future direct imaging surveys
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