Now showing 1 - 10 of 30
  • Publication
    EduCube: The 1U Educational CubeSat
    EduCube is a 1U Cubesat developed specifically for educational purposes. It is used in a hands-on training laboratory for Masters students to allow them to gain familiarity with the satellite subsystems found in a Cubesat. The students work in groups, following a set of exercises and also devising their own experiments. EduCube was designed and built in-house and is largely compliant with the Cal Poly standard.
      321
  • Publication
    The accretion/ejection paradigm of low mass stars tested with HST
    In the last few years new investigation techniques have allowed us to study in depth the spectacular phenomenon of protostellar jets, and to test the validity of the proposed models for their acceleration. In this contribution we review the current knowledge on the subject, with a special emphasis on the recent achievements obtained thanks to observations at high angular resolution, like those performed at subarcsecond scales with the Hubble Space Telescope. These results have made us able to define more clearly the morphology, kinematics, excitation of the flows on small scales, and, in turn, to derive stringent constraints for the physical processes at work. The novel information acquired puts us in a very good position to plan theoretical and observational studies aimed at understanding if similar accretion/ejection processes are also at work during the formation of Brown Dwarfs. If scaled-down versions of Herbig-Haro jets are found associated to these objects, then it would mean that the wellknown formation scenario of solar–mass stars is truly universal.
      72
  • Publication
    A combined MUSE/X-Shooter study of the TH28 jet
    (Società Astronomica Italiana, 2017-06-09) ; ; ; ;
    Here we present the first results from a MUSE/X-Shooter study of the jet from the classical T Tauri star TH 28. The combination of MUSE and X-Shooter enables us to take advantage of both spectro-imaging and broadband spectroscopy to comprehensively investigate the TH 28 jet. We present a MUSE spectro-image and PV plot of the Hα emission line and use flux ratios from the X-Shooter spectrum to estimate the mass accretion rate at log(Ṁacc) = -9.4. Future work will focus on diagnostic analyses on both sets of data, including estimating the mass outflow rate (Ṁout) and the extinction of the jet.
      134
  • Publication
    The near-UV: The true window on jet rotation
    (Società Astronomica Italiana, 2017-01-01) ; ; ;
    High resolution observations of jet rotation in newly forming stars have the potential to support theories of magneto-centrifugal jet launching. We report a detection of a radial velocity difference across the blue-shifted jet from RY Tau, the direction of which matches the CO disk rotation sense. Now, in 3 of 3 cases, the sense of the near-UV jet gradient matches the disk rotation sense, implying that we are indeed observing jet rotation. It seems the jet core, probed at near-UV wavelengths, is protected by the outer jet layers from kinematic contaminations, and thus represents the only true window on jet rotation.
      176
  • Publication
    GIARPS/GRAVITY Survey: Broad-Band 0.44–2.4 Micron High-Resolution Spectra of T-Tauri and Herbig AeBe Stars – Combining High Spatial and High Spectral Resolution Data to Unveil the Inner Disc Physics
    The GIARPS/GRAVITY survey aims to obtain a set of high spatial and spectral resolution data for a sample of T-Tauri and Herbig AeBe stars (∼100 objects) selected from the VLTI/GRAVITY GTO sample of Young Stellar Objects (YSOs). GIARPS is a broad-band spectrometer combining HARPS-N and GIANO which allows high-resolution spectra from 0.44 μm (R ∼ 115, 000) to 2.44 μm (R ∼ 50, 000) in one observation. By combining this high spectral resolution with the high spatial resolution (∼1 mas) of GRAVITY, a view of unprecedented detail can be obtained of the innermost regions of circumstellar discs in YSOs spanning a wide range of masses (0.1–5 M⊙) and ages (105–107 yr). The ultimate goal is to model the accretion and ejection mechanisms, and study how they evolve as a function of YSO mass and age, using the spatially and spectrally resolved atomic and molecular lines from the inner gaseous regions.
      277
  • Publication
    What elements of a community help undergraduates gain confidence?
    Women's underrepresentation in the field of physics continues to be an issue, in part because of the perceptions women may have about their abilities to study physics. In this paper, we will study undergraduate students' perceptions about the required level of competence for studying physics, and how these perceptions may change due to participation in spaces that support competence building. We use a mixed methods approach to look at survey responses collected from students on the Foundations of physics course at University College Dublin, and interviews with physics undergraduate facilitators of an informal program that explore the overlaps of physics and music. We hypothesise, that female students perceive the required level of competence to study physics to be higher than male students. We propose that providing formal and informal spaces that support competence building will improve undergraduate students' perceptions of their competence to study physics.
      151
  • Publication
    A search for consistent jet and disk rotation signatures in RY tau
    We present a radial velocity study of the RY Tau jet-disk system, designed to determine whether a transfer of angular momentum from disk to jet can be observed. Many recent studies report on the rotation of T Tauri disks and on what may be a signature of T Tauri jet rotation. However, due to observational difficulties, few studies report on both disk and jet within the same system to establish if the senses of rotation match and hence can be interpreted as a transfer of angular momentum. We report a clear signature of Keplerian rotation in the RY Tau disk, based on Plateau de Bure observations. We also report on the transverse radial velocity profile of the RY Tau jet close to the star. We identify two distinct profile shapes: a v-shape, which appears near jet shock positions, and a flat profile, which appears between shocks. We do not detect a rotation signature above 3σ uncertainty in any of our transverse cuts of the jet. Nevertheless, if the jet is currently in steady-state, the errors themselves provide a valuable upper limit on the jet toroidal velocity of 10 km s-1, implying a launch radius of ≤0.45 AU. However, possible contamination of jet kinematics, via shocks or precession, prevents any firm constraint on the jet launch point, since most of its angular momentum could be stored in magnetic form rather than in rotation of matter.
    Scopus© Citations 24  255
  • Publication
    Unveiling the Role of Jets in Star Formation
    We describe the role of HST in providing the first and long-awaited observational backing for the role of bipolar jets in the star formation process.
      228
  • Publication
    Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
    Context. Stellar jets are believed to play a key role in star formation, but the question of how they originate is still being debated. Aims. We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. Methods. We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. In this way, we produced a 3D map (2D in space and 1D in velocity) of the jet's physical parameters i.e. electron density ne, hydrogen ionisation fraction xe, and total hydrogen density nH. The method used is a new version of the BE-technique. Results. A fundamental improvement is that the new diagnostic method allows us to overcome the upper density limit of the standard [S≠ii] diagnostics. As a result, we find at the base of the jet high electron density, ne ~ 105, and very low ionisation, xe ~ 0.02-0.05, which combine to give a total density up to n H ~ 3 × 106. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of xe from 0.05 to a plateau at 0.7 downstream at 2" from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. No evidence was found of variations in the parameters across the jet, within a given velocity interval. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, Mj, in the blue-shifted lobe in different velocity channels, that contribute to a total of Mj ~ 8±4 × 10-9 M⊙yr-1. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of L̇ j ~ 2.9 ± 1.5 × 10-6 M ⊙yr-1 AU km s-1. We discuss implications of these findings for jet launch theories. Conclusions. The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution.
    Scopus© Citations 30  283
  • Publication
    Measuring the ionisation fraction in a jet from a massive protostar
    It is important to determine if massive stars form via disc accretion, like their low-mass counterparts. Theory and observation indicate that protostellar jets are a natural consequence of accretion discs and are likely to be crucial for removing angular momentum during the collapse. However, massive protostars are typically rarer, more distant and more dust enshrouded, making observational studies of their jets more challenging. A fundamental question is whether the degree of ionisation in jets is similar across the mass spectrum. Here we determine an ionisation fraction of ~5–12% in the jet from the massive protostar G35.20-0.74N, based on spatially coincident infrared and radio emission. This is similar to the values found in jets from lower-mass young stars, implying a unified mechanism of shock ionisation applies in jets across most of the protostellar mass spectrum, up to at least ~10 solar masses.
    Scopus© Citations 15  404