Deep into the core of dense star clusters: an astrometric and photometric test case for ELT

2020 ◽  
Vol 494 (3) ◽  
pp. 4413-4425
Author(s):  
G Fiorentino ◽  
M Bellazzini ◽  
M Spera ◽  
N B Sabha ◽  
M Mapelli ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Large Magellanic Cloud ◽  
Young Star ◽  
Integration Time ◽  
Test Case ◽  
Limited Data ◽  
Technical Specifications ◽  
Motion Measurements ◽  
Ao Mode ◽  
Total Integration

ABSTRACT We present a novel analysis of a young star cluster in the Large Magellanic cloud, R136-like, as seen by the Extremely Large Telescope (ELT). The main aim of this study is to quantify precision and accuracy of stellar proper motion measurements in crowded field when using an ELT working at its diffraction limit. This can serve as a reference study for future development of ELT scientific cases. In particular, we investigate our future ability to detect the dynamical signature of intermediate-mass black holes (IMBHs) with mass ∼104 M⊙ through detailed measurements of stellar proper motions. We have simulated two N-body dynamical cluster models with and without an IMBH. For each model, we have chosen two snapshots temporally spaced by 5 yr. Stellar fluxes in IJHK filters and star positions have been used to create ELT mock images for both single- and multiconjugate adaptive optics observing modes following the requierements given by ESO technical specifications for the first light imager. These images have been analysed using a classical software for seeing-limited data reduction, daophot/allstar. We make accurate photometry till the very faint pre-main-sequence stars, i.e. depending on the adaptive optics (AO) mode, magnitudes down to K ∼ 24 mag (single-conjugate AO) or K ∼ 22 mag (multiconjugate AO) in a total integration time of 20 min on target. Although daophot suite of programs is not devoted to precise astrometry, the astrometric accuracy is impressive, reaching few μas yr−1 or km s−1. In these assumptions, we are able to detect the IMBH signature at the centre of the cluster.

scholarly journals Near IR Astrometry of Magnetars

2012 ◽  
Vol 8 (S291) ◽  
pp. 514-516
Author(s):  
Shriharsh P. Tendulkar
Keyword(s):  
Adaptive Optics ◽  
Proper Motion ◽  
Young Star ◽  
Proper Motions ◽  
Near Ir ◽  
Upper Limit ◽  
Motion Measurements ◽  
Guide Star ◽  
Laser Guide ◽  
Young Star Clusters

AbstractWe report on the progress of our five-year program for astrometric monitoring of magnetars using high-resolution NIR observations using the laser guide star adaptive optics (LGS-AO) supported NIRC2 camera on the 10-meter Keck telescope. We have measured the proper motion of two of the youngest magnetars, SGR 1806–20 and SGR 1900+14, which have counterparts with K ~21 mag, and have placed a preliminary upper limit on the motion of the young AXP 1E 1841–045. The precision of the proper motion measurement is at the milliarcsecond per year level. Our proper motion measurements now provide evidence to link SGR 1806–20 and SGR 1900+14 with neighboring young star clusters. At the distances of these magnetars, their proper motion corresponds to transverse space velocities of 350 ± 100 km s−1 and 130 ± 30 km s−1 respectively. The upper limit on the proper motion of AXP 1E 1841–045 is 160 km s−1. With the sample of proper motions available, we conclude that the kinematics of the magnetar family are not distinct from that of pulsars.

scholarly journals High-contrast and resolution near-infrared photometry of the core of R136

2021 ◽  
Vol 503 (1) ◽  
pp. 292-311
Author(s):  
Zeinab Khorrami ◽  
Maud Langlois ◽  
Paul C Clark ◽  
Farrokh Vakili ◽  
Anne S M Buckner ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Near Infrared ◽  
Outer Region ◽  
Mass Range ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Star Forming ◽  
The Core ◽  
Very Large Telescope ◽  
30 Doradus

ABSTRACT We present the sharpest and deepest near-infrared photometric analysis of the core of R136, a newly formed massive star cluster at the centre of the 30 Doradus star-forming region in the Large Magellanic Cloud. We used the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode for the second time with longer exposure time in the H and K filters. Our aim was to (i) increase the number of resolved sources in the core of R136, and (ii) to compare with the first epoch to classify the properties of the detected common sources between the two epochs. Within the field of view (FOV) of 10.8″ × 12.1″ ($2.7\,\text {pc}\times 3.0\, \text {pc}$), we detected 1499 sources in both H and K filters, for which 76 per cent of these sources have visual companions closer than 0.2″. The larger number of detected sources enabled us to better sample the mass function (MF). The MF slopes are estimated at ages of 1, 1.5, and 2 Myr, at different radii, and for different mass ranges. The MF slopes for the mass range of 10–300 M⊙ are about 0.3 dex steeper than the mass range of 3–300 M⊙, for the whole FOV and different radii. Comparing the JHK colours of 790 sources common in between the two epochs, 67 per cent of detected sources in the outer region (r > 3″) are not consistent with evolutionary models at 1–2 Myr and with extinctions similar to the average cluster value, suggesting an origin from ongoing star formation within 30 Doradus, unrelated to R136.

Snapshot Imaging with the Australia Telescope Compact Array

1995 ◽  
Vol 12 (2) ◽  
pp. 227-238 ◽  
Author(s):  
A. M. Burgess ◽  
R. W. Hunstead
Keyword(s):  
Dynamic Range ◽  
Angular Size ◽  
Integration Time ◽  
More Care ◽  
Snapshot Imaging ◽  
The One ◽  
5 Ghz ◽  
Total Integration ◽  
Deconvolution Techniques ◽  
Compact Array

AbstractRadio snapshot imaging is an efficient observing method which allows several sources to be observed in the one session. Snapshot observing with the Australia Telescope Compact Array (ATCA) involves special difficulties, as the small number of antennas combined with the short total integration time leads to high sidelobe levels in the raw images. The images can be improved markedly by standard deconvolution techniques, but more care is required in their use because of the difficulty in distinguishing real emission from artefacts. This study, based on a set of snapshot observations of strong sources at 5 GHz, gives guidance on both the planning of observations and the data reduction. We show that snapshot imaging with the 6 km ATCA can achieve a dynamic range of 100–200:1 provided certain conditions are met, namely a peak flux density > 100 mJy, an angular size ≤ 30″ and an hour-angle coverage spanning at least six well-separated 5-minute cuts. When observing weak sources it is essential for calibration sources to be selected carefully and observed frequently.

Regional Bicycle Network Evaluation and Strategic Planning: A Quantitative Methodological Approach Despite Limited Data Sources for Cycling

2021 ◽  
pp. 036119812110288
Author(s):  
Alex van Dulmen ◽  
Martin Fellendorf
Keyword(s):  
Travel Demand ◽  
Choice Model ◽  
Methodological Approach ◽  
Data Availability ◽  
Data Sources ◽  
Test Case ◽  
Demand Model ◽  
Limited Data ◽  
Demand Models ◽  
Bicycle Infrastructure

In cases where budgets and space are limited, the realization of new bicycle infrastructure is often hard, as an evaluation of the existing network or the benefits of new investments is rarely possible. Travel demand models can offer a tool to support decision makers, but because of limited data availability for cycling, the validity of the demand estimation and trip assignment are often questionable. This paper presents a quantitative method to evaluate a bicycle network and plan strategic improvements, despite limited data sources for cycling. The proposed method is based on a multimodal aggregate travel demand model. Instead of evaluating the effects of network improvements on the modal split as well as link and flow volumes, this method works the other way around. A desired modal share for cycling is set, and the resulting link and flow volumes are the basis for a hypothetical bicycle network that is able to satisfy this demand. The current bicycle network is compared with the hypothetical network, resulting in preferable actions and a ranking based on the importance and potentials to improve the modal share for cycling. Necessary accompanying measures for other transport modes can also be derived using this method. For example, our test case, a city in Austria with 300,000 inhabitants, showed that a shift of short trips in the inner city toward cycling would, without countermeasures, provide capacity for new longer car trips. The proposed method can be applied to existing travel models that already contain a mode choice model.

scholarly journals Filamentary Nebulosity Surrounding M87

1987 ◽  
Vol 117 ◽  
pp. 216-217
Author(s):  
S. van den Bergh ◽  
C. J. Pritchet
Keyword(s):  
Broad Band ◽  
Integration Time ◽  
The Difference ◽  
Total Integration

Recently we have obtained both Hα + [NII] and broad-band red exposures of a number of galaxies with an RCA 320 × 512 CCD at the prime-focus of the 3.6 m CFH Telescope. Figure 1 shows the difference between Hα and red exposures (each with a total integration time of 60 min) of M87 = NGC4486.

scholarly journals Morphology of z ~ 1 galaxies from deep K-band AO imaging

2006 ◽  
Vol 2 (S235) ◽  
pp. 405-405
Author(s):  
Marc Huertas-Company ◽  
Daniel Rouan ◽  
Geneviève Soucail ◽  
Olivier Le Fèvre ◽  
Lidia Tasca
Keyword(s):  
Adaptive Optics ◽  
Spatial Resolution ◽  
Near Infrared ◽  
High Spatial Resolution ◽  
Integration Time ◽  
Early Type ◽  
Distant Galaxies ◽  
First Time ◽  
Concentration Asymmetry ◽  
Adaptive Optics System

AbstractWe present the results of observations of distant galaxies (z ~ 0.8) at high spatial resolution (~0.1"). We observed 7 fields of 1' × 1' with the NACO Adaptive Optics system (VLT) in Ks (2.2μm) band with typical V ~ 14 guide stars and 3h integration time per field. Observed fields are selected within the COSMOS survey area. We analyze the morphologies by means of B/D (Bulge/Disk) decomposition with GIM2D and CAS (Concentration-Asymmetry) estimators for 79 galaxies with magnitudes between Ks = 17 − 23 and classify them in three main morphological types (Late Type, Early Type and Irregulars). We obtain for the first time an estimate of the distribution of galaxy types at redshift z ~ 1 as measured from the near infrared at high spatial resolution.

Discovery of a Luminous White Dwarf in a Young Star Cluster in the Large Magellanic Cloud

1998 ◽  
Vol 499 (1) ◽  
pp. L53-L56 ◽  
Author(s):  
Rebecca A. W. Elson ◽  
Steinn Sigurdsson ◽  
Jarrod Hurley ◽  
Melvyn B. Davies ◽  
Gerard F. Gilmore
Keyword(s):  
White Dwarf ◽  
Large Magellanic Cloud ◽  
Young Star ◽  
Magellanic Cloud ◽  
Star Cluster

Numerical Simulation of Heavy Particle Dispersion Time Step and Nonlinear Drag Considerations

1992 ◽  
Vol 114 (1) ◽  
pp. 100-106 ◽  
Author(s):  
Lian-Ping Wang ◽  
D. E. Stock
Keyword(s):  
Numerical Simulation ◽  
Numerical Experiments ◽  
Heavy Particle ◽  
Free Fall ◽  
Particle Dispersion ◽  
Integration Time ◽  
Fall Velocity ◽  
Time Step ◽  
Physical Experiments ◽  
Total Integration

Numerical experiments can be used to study heavy particle dispersion by tracking particles through a numerically generated instantaneous turbulent flow field. In this manner, data can be generated to supplement physical experiments. To perform the numerical experiments efficiently and accurately, the time step used when tracking the particles through the fluid must be chosen correctly. After finding a suitable time step for one particular simulation, the time step must be reduced as the total integration time increases and as the free-fall velocity of the particle increases. Based on the numerical calculations, we suggest that the nonlinear drag be included in a numerical simulation if the ratio of the particle’s Stokes free-fall velocity to the fluid rms velocity is greater than two.

scholarly journals Searching for Hα emitting sources around MWC 758

2018 ◽  
Vol 613 ◽  
pp. L5 ◽  
Author(s):  
N. Huélamo ◽  
G. Chauvin ◽  
H. M. Schmid ◽  
S. P. Quanz ◽  
E. Whelan ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Mass Range ◽  
Position Angle ◽  
Central Star ◽  
Young Star ◽  
Upper Limit ◽  
T Tauri ◽  
Very Large Telescope ◽  
Accretion Rates ◽  
Differential Imaging

Context. MWC 758 is a young star surrounded by a transitional disk. The disk shows an inner cavity and spiral arms that could be caused by the presence of protoplanets. Recently, a protoplanet candidate has been detected around MWC 758 through high-resolution L′-band observations. The candidate is located inside the disk cavity at a separation of ~111 mas from the central star, and at an average position angle of ~165.5°. Aims. We aim at detecting accreting protoplanet candidates within the disk of MWC 758 through angular spectral differential imaging (ASDI) observations in the optical regime. In particular, we explore the emission at the position of the detected planet candidate. Methods. We have performed simultaneous adaptive optics observations in the Hα line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT). Results. The data analysis does not reveal any Hα signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5σ upper limit of ~7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a Hα line luminosity of LHα ≲ 5×10−5 L⊙ at 111 mas. Assuming that LHα scales with Lacc as in classical T Tauri stars (CTTSs) as a first approximation, we can estimate an accretion luminosity of Lacc < 3.7 × 10−4 L⊙ for the protoplanet candidate. For the predicted mass range of MWC 758b, 0.5–5 MJup, this implies accretion rates smaller than Ṁ < 3.4 × (10−8−10−9)M⊙ yr−1, for an average planet radius of 1.1 RJup. Therefore, our estimates are consistent with the predictions of accreting circumplanetary accretion models for Rin = 1RJup. The ZIMPOL line luminosity is consistent with the Hα upper limit predicted by these models for truncation radii ≲3.2 RJup. Conclusions. The non-detection of any Hα emitting source in the ZIMPOL images does not allow us to unveil the nature of the L′ detected source. Either it is a protoplanet candidate or a disk asymmetry.

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