Now showing 1 - 10 of 30
- PublicationA combined MUSE/X-Shooter study of the TH28 jetHere 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.
- PublicationThe near-UV: The true window on jet rotationHigh 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.
- PublicationX-RED: A satellite mission concept to detect early universe gamma ray burstsGamma ray bursts (GRBs) are the most energetic eruptions known in the Universe. Instruments such as Compton-GRO/BATSE and the GRB monitor on BeppoSAX have detected more than 2700 GRBs and, although observational confirmation is still required, it is now generally accepted that many of these bursts are associated with the collapse of rapidly spinning massive stars to form black holes. Consequently, since first generation stars are expected to be very massive, GRBs are likely to have occurred in significant numbers at early epochs. X-red is a space mission concept designed to detect these extremely high redshifted GRBs, in order to probe the nature of the first generation of stars and hence the time of reionisation of the early Universe. We demonstrate that the gamma and x-ray luminosities of typical GRBs render them detectable up to extremely high redshifts (z ∼ 10 to 30), but that current missions such as HETE2 and SWIFT operate outside the observational range for detection of high redshift GRB afterglows. Therefore, to redress this, we present a complete mission design from the science case to the mission architecture and payload, the latter comprising three instruments, namely wide field x-ray cameras to detect high redshift gamma-rays, an x-ray focussing telescope to determine accurate coordinates and extract spectra, and an infrared spectrograph to observe the high redshift optical afterglow. The mission is expected to detect and identify for the first time GRBs with z > 10, thereby providing constraints on properties of the first generation of stars and the history of the early Universe.
- PublicationThe accretion/ejection paradigm of low mass stars tested with HSTIn 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.
- PublicationThe Enigma of Jets and Outows from Young Stars(Astronomical Society of India, 2011-07-01)Research in recent decades has seen many important advances in understanding the role of jets and outflows in the star formation process. Although, many open issues still remain, multi-wavelength high resolution observations have provided unprecedented insights into these bizarre phenomena. An overview of some of the current research is given, in which great strides have been made in addressing fundamental questions such as: how are jets generated? what is the jet acceleration mechanism? how are jets collimated? what is the relationship between accretion and ejection? how does mass accretion proceed? do jets somehow extract angular momentum? and finally, is there a universal mechanism for jet generation on all scales from brown dwarfs to AGNs?
- PublicationJet rotation: Launching region, angular momentum balance and magnetic properties in the bipolar outflow from RW AurUsing STIS on board the HST we have obtained a spectroscopic map of the bipolar jet from RW Aur with the slit parallel to the jet axis and moved across the jet in steps of 0″.07. After applying a velocity correction due to uneven slit illumination we find signatures of rotation within the first 300 AU of the jet (1″.5 at the distance of RW Aur). Both lobes rotate in the same direction (i.e. with different helicities), with toroidal velocities in the range 5-30 km s-1 at 20 and 30 AU from the symmetry axis in the blueshifted and redshifted lobes, respectively. The sense of rotation is anti-clockwise looking from the tip of the blue lobe (PA 130° north to east) down to the star. Rotation is more evident in the [OI] and [NII] lines and at the largest sampled distance from the axis. These results are consistent with other STIS observations carried out with the slit perpendicular to the jet axis, and with theoretical simulations. Using current magneto-hydrodynamic models for the launch of the jets, we find that the mass ejected in the observed part of the outflow is accelerated from a region in the disk within about 0.5 AU from the star for the blue lobe, and within 1.6 AU from the star for the red lobe. Using also previous results we estimate upper and lower limits for the angular momentum transport rate of the jet. We find that this can be a large fraction (two thirds or more) of the estimated rate transported through the relevant portion of the disk. The magnetic lever arm (defined as the ratio r A/r0 between the Alfvèn and footpoint radii) is in the range 3.5-4.6 (with an accuracy of 20-25%), or, alternatively, the ejection index ξ = d ln(Ṁacc)/dr is in the range 0.025-0.046 (with similar uncertainties). The derived values are in the range predicted by the models, but they also suggest that some heating must be provided at the base of the flow. Finally, using the general disk wind theory we derive the ratio Bφ/Bp of the toroidal and poloidal components of the magnetic field at the observed location (i.e. about 80-100 AU above the disk). We find this quantity to be 3.8 ± 1.1 at 30 AU from the axis in the red lobe and -8.9 ± 2.7 at 20 AU from the axis in the blue lobe (assuming cylindrical coordinates centred on the star and with positive z along the blue lobe). The toroidal component appears to be dominant, which would be consistent with magnetic collimation of the jet. The field appears to be more tightly wrapped on the blue side. © ESO 2005.
164Scopus© Citations 85
- PublicationEduCube: The 1U Educational CubeSatEduCube 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.
- PublicationWhat 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.
- PublicationSearching for Jet Rotation Signatures in Class 0 and I JetsIn recent years, there has been a number of detections of asymmetries in the radial velocity profile across jets from young stars. The significance of these results is considerable. They may be interpreted as a signature of jet rotation about its symmetry axis, thereby representing the only existing observational indications supporting the theory that jets extract angular momentum from star-disk systems. However, the possibility that we are indeed observing jet rotation in pre-main sequence systems is undergoing active debate. To test the validity of a rotation argument, we must extend the survey to a larger sample, including younger sources. We present the latest results of a radial velocity analysis on jets from Class 0 and I sources, using high resolution data from the infrared spectrograph GNIRS on GEMINI South. These observations demonstrate the difficulty of conducting this study from the ground, and highlight the necessity for high angular resolution via adaptive optics or space-based facilities.
- PublicationMeasuring the ionisation fraction in a jet from a massive protostarIt 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.
217Scopus© Citations 11