arXiv subjects

K. Leech

Publications and source records attributed to K. Leech.

17 recordsLinked to original sources

arXiv2021

From nuclei to neutron stars: simple binding energy computer modelling in the classroom (part 2)

We introduce two simple online activities to explore the physics of neutron stars. These provide an introduction to the basic properties of compact objects, like their masses and radii, for secondary school students. The first activity explores the idea of the minimum mass of a neutron star. It is directly linked to the concept of binding energy and follows on from our previous activities. The second activity focuses on the maximum mass of neutron stars using a solvable model of the neutron star interior. The activities are based on spreadsheets, provided as Supplementary Material, and can be easily adapted to different levels, age groups and discussion topics. In particular, these activities can naturally lead towards discussions on extrapolations and limits of theoretical models.

nucl-th↗

arXiv2021

From nuclei to neutron stars: simple binding energy computer modelling in the classroom (Part 1)

We present a simple activity based on the liquid-drop model which allows secondary school students to explore the uses of mathematical models and gain an intuitive understanding of the concept of binding energy, and in particular the significance of positive binding energy. Using spreadsheets provided as Supplementary Material, students can perform simple manipulations on the different coefficients of the model to understand the role of each of its five terms. Students can use the spreadsheets to determine model parameters by optimising the agreement with real atomic mass data. %This will subsequently be used to predict the limit of existence of the Segré chart and to find the minimum mass of a neutron star. This activity can be used as the starting point of a discussion about theoretical models, their validation when it comes to describing experimental data and their predictive power towards unexplored regimes.

nucl-th↗

arXiv2016

Binding Blocks: building the Universe one nucleus at the time

We present a new teaching and outreach activity based around the construction of a three-dimensional chart of isotopes using LEGO$^{\circledR}$ bricks. The activity, \emph{Binding Blocks}, demonstrates nuclear and astrophysical processes through a seven-meter chart of all nuclear isotopes, built from over 26,000 LEGO$^{\circledR}$ bricks. It integrates A-level and GCSE curricula across areas of nuclear physics, astrophysics, and chemistry, including: nuclear decays (through the colours in the chart); nuclear binding energy (through tower heights); production of chemical elements in the cosmos; fusion processes in stars and fusion energy on Earth; as well as links to medical physics, particularly diagnostics and radiotherapy.

physics.ed-ph↗

arXiv2005

ISO observations of the interacting galaxy Markarian 297: with the powerful supernova remnant 1982aa

Markarian (Mkn) 297 is a complex system with two interacting galaxies. Observations were made with ISO using ISOCAM, ISOPHOT and LWS. We present ISOCAM maps at 6.7, 7.7, 12 and 14.3 microns which, with PHT-S spectrometry of the central interacting region, probe the dust obscured star formation and dust properties. ISOCAM reveals that the strongest emission region in the four MIR bands is completely unremarkable at visible and near-IR (e.g. 2MASS) wavelengths, and does not coincide with the nuclear region of either colliding galaxy. It shares this striking characteristic with the overlap region of the colliding galaxies in the Antennae (NGC 4038, 4039), the intragroup region of Stephan's Quintet, and IC 694 in the interacting system Arp 299. At 15 microns, the hidden source in Mkn 297 is, respectively, 14.6 and 3.8 times more luminous than the hidden sources in the Antennae (NGC 4038/4039) and Stephan's Quintet. Numerical simulations indicate that we see the Mkn 297 interaction about 1.5 x 10e8 years after the collision. ISOCAM shows knots and ridges of emission. The 14.3/7.7 micron ratio map implies widespread strong star formation. Strong emission features were detected in the ISOPHOT spectrum, while [OI], [OIII] and [CII] emission lines were seen with LWS. Using data from the three instruments, luminosities and masses for two dust components were determined. The total infrared luminosity is approximately 10e11 L_sol, marginally a LIRG. A 1979 supernova generated one of the most powerful known radio remnants (SN 1982aa) close to the strongest MIR source and identified with star forming region 14 in the optical. This exceptional supernova explosion may have been accompanied by a GRB, and a search for a GRB in this direction in contemporaneous satellite data is recommended.

astro-ph↗

arXiv2004

An ISOCAM survey through gravitationally lensing galaxy clusters. II. The properties of infrared galaxies in the A2218 field

We observed the cluster Abell 2218 (z=0.175), with ISOCAM on board the Infrared Space Observatory, using two filters with reference wavelengths of 6.7 and 14.3 microns. We detected 67 extragalactic mid-infrared sources. Using the ``GRASIL'' models of Silva et al. (1998) we have obtained acceptable and well constrained fits to the observed spectral energy distributions (SEDs) of 41 of these sources, for which additional optical/near-infrared magnitudes, and, in some cases, redshifts, were available. We have then determined the total infrared luminosities and star formation rates (SFRs) of these 41 sources, of which 27 are cluster members and 14 are field galaxies at a median redshift z~0.6. The SEDs of most of the ISOCAM cluster members are best fit by models with negligible star formation in the last ~1 Gyr. The 7 faintest cluster members have a slightly higher, but still very mild, star-formation activity. The ISOCAM-selected cluster galaxies appear to be an unbiased subsample of the overall cluster population. If A2218 is undergoing a merger, as suggested by some optical and X-ray analyses, then this merger does not seem to affect the mid-infrared properties of its galaxies. The SEDs of most ISOCAM-selected field sources are best fit by models with significant ongoing (and recent) star formation, resembling those of massive star-forming spirals or (post)starburst galaxies. Their median SFR is 22 solar masses per year. Eight of the 14 field sources are Luminous IR Galaxies. (Abridged)

astro-ph↗

arXiv2003

An ISOCAM survey through gravitationally lensing galaxy clusters

ISOCAM was used to perform a deep survey through three gravitationally lensing clusters of galaxies. Nearly seventy sq. arcmin were covered over the clusters A370, A2218 and A2390. We present maps and photometry at 6.7 & 14.3 microns, showing a total of 145 mid-IR sources and the associated source counts. The 15 micron counts reach the faintest level yet recorded. All sources have counterparts in the optical or near-IR. Models of the clusters were used to correct for the effects of lensing, which increases the sensitivity of the survey. Seven of fifteen SCUBA sources were detected at 15 microns. Five have redshift between 0.23 & 2.8, with a median of 0.9. The field sources were counted to a lensing-corrected sensitivity of 30 microJy at 15 microns, and 14 microJy at 7 microns. The counts, corrected for completeness, contamination by cluster sources and lensing, confirm and extend findings of an excess by a factor of ten in the 15 micron population with respect to source models with no evolution. Source redshifts are mostly between 0.4 and 1.5. For the counts at 7 microns, integrating from 14 microJy to 460 microJy, we resolve 0.49+/-0.2 nW.m^(-2).sr^(-1) of the infrared background light (IBL) into discrete sources. At 15 microns we include the counts from other ISOCAM surveys to integrate from 30 microJy to 50 mJy, two to three times deeper than unlensed surveys, to resolve 2.7+/-0.62 nW.m^(-2).sr^(-1) of the IBL. These values are 10% and 55%, respectively, of the upper limit to the IBL, derived from photon-photon pair production of the TeV gamma rays from BL-Lac sources on the IBL photons. However, recent detections of TeV gamma rays from the z=0.129 BL Lac H1426+428 suggest that the 15 micron background reported implies substantial absorption of TeV photons from that source.

astro-ph↗

arXiv2002

ISO observations of Hickson Compact Group 31 with the central Wolf-Rayet galaxy NGC 1741

Hickson Compact Group (HCG) 31, consisting of the Wolf-Rayet galaxy NGC 1741 and its irregular dwarf companions, was observed using the Infrared Space Observatory. The deconvolved ISOCAM maps of the galaxies using the 7.7 micron and 14.3 micron (LW6 and LW3) filters are presented, along with ISOPHOT spectrometry of the central starburst region of NGC 1741 and the nucleus of galaxy HCG 31A. Strong mid-IR emission was detected from the central burst in NGC 1741, along with strong PAH features and a blend of features including [S IV] at 10.5 micron. The 14.3/6.75 micron flux ratio, where the 6.75 micron flux was synthesized from the PHT-S spectrum, and 14.3/7.7 micron flux ratios suggest that the central burst within NGC 1741 may be moving towards the post-starburst phase. Diagnostic tools including the ratio of the integrated PAH luminosity to the 40 to 120 micron infrared luminosity and the far-infrared colours reveal that despite the high surface brightness of the nucleus, the properties of NGC 1741 can be explained in terms of a starburst and do not require the presence of an AGN. The Tycho catalogue star TYC 04758-466-1, with m$_{V}$ = 11.3 and spectral type F6, was detected at 7.7 and 14.3 microns.

astro-ph↗

arXiv2000

Incidence and survival of remnant disks around main-sequence stars

We present photometric ISO 60 and 170um measurements, complemented by some IRAS data at 60um, of a sample of 84 nearby main-sequence stars of spectral class A, F, G and K in order to determine the incidence of dust disks around such main-sequence stars. Of the stars younger than 400 Myr one in two has a disk; for the older stars this is true for only one in ten. We conclude that most stars arrive on the main sequence surrounded by a disk; this disk then decays in about 400 Myr. Because (i) the dust particles disappear and must be replenished on a much shorter time scale and (ii) the collision of planetesimals is a good source of new dust, we suggest that the rapid decay of the disks is caused by the destruction and escape of planetesimals. We suggest that the dissipation of the disk is related to the heavy bombardment phase in our Solar System. Whether all stars arrive on the main sequence surrounded by a disk cannot be established: some very young stars do not have a disk. And not all stars destroy their disk in a similar way: some stars as old as the Sun still have significant disks.

astro-ph↗

arXiv2000

ISO observations of the Wolf-Rayet galaxy NGC 7714 and its companion object NGC 7715

The interacting system Arp 284 consisting of the Wolf-Rayet galaxy NGC 7714 and its irregular companion NGC 7715 was observed using the Infrared Space Observatory. Deconvolved ISOCAM maps of the galaxies using the 14.3, 7.7 and 15 micron LW3, LW6 and LW9 filters, along with ISOPHOT spectrometry of the nuclear region of NGC 7714 were obtained and are presented. Strong ISOCAM emission was detected from the central source in NGC 7714, along with strong PAH features, the emission line [Ar II], molecular hydrogen at 9.66 microns and a blend of features including [S IV] at 10.6 microns. IR emission was not detected from the companion galaxy NGC 7715, the bridge linking the two galaxies or from the partial stellar ring in NGC 7714 where emission ceases abruptly at the interface between the disk and the ring. The morphology of the system can be well described by an off-centre collision between the two galaxies. The LW3/LW2, where the LW2 flux was synthesized from the PHOT-SL spectrum, LW9/LW6 and LW3/LW6 ratios suggest that the central burst within NGC 7714 is moving towards the post-starburst phase, in agreement with the age of the burst. Diagnostic tools including the ratio of the integrated PAH luminosity to the 40 to 120 microns infrared luminosity and the far-infrared colours reveal that despite the high surface brightness of the nucleus, the properties of NGC 7714 can be explained in terms of a starburst and do not require the prescence an AGN.

astro-ph↗

arXiv2000

ISO observations of a sample of 60 micron peaker galaxies

The sample of IRAS galaxies with spectral energy distributions that peak near 60 microns are called Sixty Micron Peakers (SMPs or 60PKs). Their generally peculiar and amorphous morphologies, hot dust and lack of a cirrus component have been interpreted as being indicative of a recent interaction/merger event. Mid-infrared spectra of eight SMPs, obtained with ISOPHOT-S in the ~2-11 micron band are presented. Four of the observed sources are H II region-like (H2) galaxies, three are Seyfert 2 and one is unclassified. Emission attributed to Polycyclic Aromatic Hydrocarbons (PAHs) at 6.2, 7.7 and 8.6 micron is ubiquitous in the spectra. The PHOT-S spectrum of the H2 galaxy IRAS 23446+1519 exhibits a bright 11.04 micron line and an 8.6 micron feature of comparable size to its 7.7 micron feature. [S IV] emission at 10.5 micron was detected in three of four H2 galaxies and in one Seyfert 2 galaxy. The ratio of the 7.7 \textmu m PAH feature to the continuum at 7.7 micron (PAH L/C) divides the eight SMPs at a ratio greater than 0.8 for H2 and less than 0.8 for Seyfert galaxies. An anti-correlation between PAH L/C and the ratio of the continuum flux at 5.9 micron to the flux at 60 micron is found, similar to that found in ultraluminous infrared galaxies. Silicate absorption at approximately 9.7 micron was observed in the Seyfert 2 galaxy, IRAS 04385-0828 and in IRAS 03344-2103. The previously unclassified SMP galaxy IRAS 03344-2103 is probably a Seyfert 2.

astro-ph↗

arXiv2000

2.5-11 micron spectroscopy and imaging of AGNs: implication for unification schemes

We present 2.5-11 micron spectrophotometric & imaging ISO observations of 28 Sf1, 29 Sf2 & 1 normal galaxy. The Sf1 & Sf2 MIR spectra are statistically different: Sf1 have a strong power-law continuum of index -0.84+/-0.24 & weak PAH emission bands. Sf2s have a weak continuum & very strong PAH emission features with EW (equivalent widths) up to 7.2 micron. On the other hand, the Sf1 and Sf2 PAH luminosities do not differ statistically and the 7 micron continuum is ~8 times less luminous in Sf2s than in Sf1s. The PAH emission is unrelated to the nuclear activity & arises in the bulge ISM. PAH EW are thus a sensitive nuclear redenning indicator. These results are consistent with unified schemes & imply that the Sf2 MIR nuclear continuum is, on the average, extinguished by 92+/-37 visual magnitudes whereas it is directly visible in Sf1s. The dispersion in Sf2's PAH EW is consistent with the expected spread in viewing angles. Those Sf2s with PAH EW > 5 micron suffer from > 125 magnitudes of extinction and are invariably weak X-ray sources. Such Sf2s represent the highly inclined objects where our line of sight intercepts the full extent of the torus. About 1/3rd of the Sf2s have PAH EW <= 2 micron, in the range of Sf1s. Among them, those which have been observed in spectropolarimetry or IR spectroscopy invariably display "hidden" broad lines. As proposed by Heisler et al (1997), such Sf2s are most likely seen at grazing incidence such that one has a direct view of both the "reflecting screen" and the torus inner wall emitting the MIR continuum. Our observations thus constrain the screen & the torus inner wall to be spatially co-located. Finally, the 9.7 micron Silicate feature appears weakly in emission in Sf1s, implying that the torus vertical thickness cannot significantly exceed E+24 cm-2

astro-ph↗

arXiv1999

An ISOCAM Mid-IR Survey through Gravitationally Lensing Galaxy Clusters

We present imaging results and source counts from a deep ISOCAM cosmological survey at 15 microns, through gravitationally lensing galaxy clusters. We take advantage of the cluster gravitational amplification to increase the sensitivity of our survey. We detect a large number of luminous mid-IR sources behind the cluster lenses, down to very faint fluxes, which would have been unreachable without the gravitational lensing effect. These source counts, corrected for lensing distortion effects and incompleteness, are in excess of the predictions of no-evolution models that fit local IRAS counts. By integrating the 15 microns source counts from our counts limit, 30 microJy, to 50 mJy we estimate the resolved mid-IR background radiation intensity.

astro-ph↗

arXiv1999

A Deep and Ultra-deep ISOCAM Cosmological Survey through Gravitationally Lensing Clusters of Galaxies

We present imaging results and source counts from an ISOCAM deep and ultra-deep cosmological survey through gravitationally lensing clusters of galaxies at 7 and 15 microns. A total area of about 53 sq.arcmin was covered in maps of three clusters. The lensing increases the sensitivity of the survey. A large number of luminous mid-infrared (MIR) sources were detected behind the lenses, and most could be unambiguously identified with visible counterparts. Thanks to the gravitational amplification, these results include the faintest MIR detections ever recorded, extending source counts to an unprecedented level. The source counts, corrected for cluster contamination and lensing distortion effects, show an excess by a factor of 10 with respect to the prediction of a no-evolution model, as we reported for A2390 alone in Altieri et al. (1999). These results support the A2390 result that the resolved 7 and 15 microns background radiation intensities are 1.7 (+/- 0.5) x 10^-9 and 3.3 (+/- 1.3) x 10^-9 W/m^2/sr, respectively, integrating from 30 microJy to 50 mJy.

astro-ph↗

arXiv1998

An ultra-deep ISOCAM observation through a cluster-lens

We present results of ultra-deep ISOCAM observations through a cluster-lens at 7 and 15 micron with the Infrared Space Observatory (ISO) satellite. These observations reveal a large number of luminous Mid-Infrared (MIR) sources. Cross-identification in the optical and Near-Infrared (NIR) wavebands shows that about half of the 7 micron sources are cluster galaxies. The other 7 micron and almost all 15 micron sources are identified as lensed distant galaxies. Thanks to the gravitational amplification they constitute the faintest MIR detected sources, allowing us to extend the number counts in both the 7 and 15 micron bands. In particular, we find that the 15 micron counts have a steep slope alpha_15 = -1.5 +/- 0.3 and are large, with N_15 (>30 microJy}) = 13 +/- 5 per square arcmin. These numbers rule out non-evolutionary models and favour very strong evolution. Down to our counts limit, we found that the resolved 7 and 15 microns background radiation intensity is respectively (2 +/-0.5) 10^(-9) and (5 +/-1) 10^(-9) W m^(-2) sr^(-1).

astro-ph↗

arXiv1998

2.5-12 micron spectrophotometry and imaging of the CfA sample

We present low resolution spectrophotometric and imaging ISO observations of a sample of 54 AGN's over the 2.5-11 micron range. The observations generally support unification schemes and set new constraints on models of the molecular torus.

astro-ph↗

arXiv1998

ISO Mid-Infrared Observations of Abell 370

We report on the mid-IR imaging at 7 and 10 microns of the galaxy cluster Abell 370, obtained with the ISOCAM instrument onboard ESA's Infrared Space Observatory (ISO), as part of an ongoing program to image gravitational arcs and arclets in distant clusters. We have recorded initial detections of the A0 giant arc in both bandpasses, the two central dominant galaxies at 7 microns, and several other cluster members and field galaxies. These preliminary results are indicative of the potential output of our program when more extensive observational data become available.

astro-ph↗

arXiv1998

Deep ISOCAM Observations of Abell 2218

We report on the mid-infrared imaging at 5, 7, 10 and 15 microns of the galaxy cluster Abell 2218 obtained with the ISOCAM instrument onboard ESA's Infrared Space Observatory (ISO), as part of an on-going program to image gravitational arcs and arclets in distant clusters. Several cluster galaxies as well as field galaxies are detected. We discuss their mid-IR flux properties.

astro-ph↗