arXiv subjects

T. P. Ray

Publications and source records attributed to T. P. Ray.

At least 37 records · Page 2Linked to original sources

arXiv2024

Ejecta, Rings, and Dust in SN 1987A with JWST MIRI/MRS

Supernova (SN) 1987A is the nearest supernova in $\sim$400 years. Using the {\em JWST} MIRI Medium Resolution Spectrograph, we spatially resolved the ejecta, equatorial ring (ER) and outer rings in the mid-infrared 12,927 days after the explosion. The spectra are rich in line and dust continuum emission, both in the ejecta and the ring. Broad emission lines (280-380~km~s$^{-1}$ FWHM) seen from all singly-ionized species originate from the expanding ER, with properties consistent with dense post-shock cooling gas. Narrower emission lines (100-170~km~s$^{-1}$ FWHM) are seen from species originating from a more extended lower-density component whose high ionization may have been produced by shocks progressing through the ER, or by the UV radiation pulse associated with the original supernova event. The asymmetric east-west dust emission in the ER has continued to fade, with constant temperature, signifying a reduction in dust mass. Small grains in the ER are preferentially destroyed, with larger grains from the progenitor surviving the transition from SN into SNR. The ER is fit with a single set of optical constants, eliminating the need for a secondary featureless hot dust component. We find several broad ejecta emission lines from [Ne~{\sc ii}], [Ar~{\sc ii}], [Fe~{\sc ii}], and [Ni~{\sc ii}]. With the exception of [Fe~{\sc ii}]~25.99$μ$m, these all originate from the ejecta close to the ring and are likely being excited by X-rays from the interaction. The [Fe~{\sc ii}]~5.34$μ$m to 25.99$μ$m line ratio indicates a temperature of only a few hundred K in the inner core, consistent with being powered by ${}^{44}$Ti decay.

astro-ph.HE↗

arXiv2024

JWST MIRI Imager Observations of Supernova SN 1987A

There exist very few mid-infrared (IR) observations of supernovae (SNe) in general. Therefore, SN 1987A, the closest visible SN in 400 years, gives us the opportunity to explore the mid-IR properties of SNe, the dust in their ejecta and surrounding medium, and to witness the birth of a SN remnant (SNR). The James Webb Space Telescope (JWST), with its high spatial resolution and extreme sensitivity, gives a new view on these issues. We report on the first imaging observations obtained with the Mid-InfraRed Instrument (MIRI). We build temperature maps and discuss the morphology of the nascent SNR. Our results show that the temperatures in the equatorial ring (ER) are quite non-uniform. This could be due to dust destruction in some parts of the ring, as had been assumed in some previous works. We show that the IR emission extends beyond the ER, illustrating the fact that the shock wave has now passed through this ring to affect the circumstellar medium on a larger scale. Finally, while sub-mm Atacama Large Millimeter Array (ALMA) observations have hinted at the location of the compact remnant of SN 1987A, we note that our MIRI data have found no such evidence.

astro-ph.SR↗

arXiv2023

JWST Observations of Young protoStars (JOYS+): Detection of icy complex organic molecules and ions. I. CH$_4$, SO$_2$, HCOO$^-$, OCN$^-$, H$_2$CO, HCOOH, CH$_3$CH$_2$OH, CH$_3$CHO, CH$_3$OCHO, CH$_3$COOH

Complex organic molecules (COMs) detected in the gas phase are thought to be mostly formed on icy grains, but no unambiguous detection of icy COMs larger than CH3OH has been reported so far. Exploring this matter in more detail has become possible with the JWST the critical 5-10 $μ$m range. In the JOYS+ program, more than 30 protostars are being observed with the MIRI/MRS. This study explores the COMs ice signatures in the low and high-mass protostar, IRAS 2A and IRAS 23385, respectively. We fit continuum and silicate subtracted observational data with IR laboratory ice spectra. We use the ENIIGMA fitting tool to find the best fit between the lab data and the observations and to performs statistical analysis of the solutions. We report the best fits for the spectral ranges between 6.8 and 8.6 $μ$m in IRAS 2A and IRAS 23385, originating from simple molecules, COMs, and negative ions. The strongest feature in this range (7.7 $μ$m) is dominated by CH4 and has contributions of SO2 and OCN-. Our results indicate that the 7.2 and 7.4 $μ$m bands are mostly dominated by HCOO-. We find statistically robust detections of COMs based on multiple bands, most notably CH3CHO, CH3CH2OH, and CH3OCHO. The likely detection of CH3COOH is also reported. The ice column density ratios between CH3CH2OH and CH3CHO of IRAS 2A and IRAS 23385, suggests that these COMs are formed on icy grains. Finally, the derived ice abundances for IRAS 2A correlate well with those in comet 67P/GC within a factor of 5. Based on the MIRI/MRS data, we conclude that COMs are present in interstellar ices, thus providing additional proof for a solid-state origin of these species in star-forming regions. The good correlation between the ice abundances in comet 67P and IRAS 2A is in line with the idea that cometary COMs can be inherited from the early protostellar phases.

astro-ph.SR↗

arXiv2023

JOYS: Disentangling the warm and cold material in the high-mass IRAS 23385+6053 cluster

(abridged) We study and compare the warm (>100 K) and cold (<100 K) material toward the high-mass star-forming region IRAS 23385+6053 (IRAS 23385 hereafter) combining high angular resolution observations in the mid-infrared (MIR) with the JWST Observations of Young protoStars (JOYS) project and with the NOEMA at mm wavelengths at angular resolutions of 0.2"-1". The spatial morphology of atomic and molecular species is investigated by line integrated intensity maps. The temperature and column density of different gas components is estimated using H2 transitions (warm and hot component) and a series of CH3CN transitions as well as 3 mm continuum emission (cold component). Toward the central dense core in IRAS 23385 the material consists of relatively cold gas and dust (~50 K), while multiple outflows create heated and/or shocked H2 and show enhanced temperatures (~400 K) along the outflow structures. An energetic outflow with enhanced emission knots of [Fe II] and [Ni II] hints at J-type shocks, while two other outflows have enhanced emission of only H2 and [S I] caused by C-type shocks. The latter two outflows are also more prominent in molecular line emission at mm wavelengths (e.g., SiO, SO, H2CO, and CH3OH). Even higher angular resolution data are needed to unambiguously identify the outflow driving sources given the clustered nature of IRAS 23385. While most of the forbidden fine structure transitions are blueshifted, [Ne II] and [Ne III] peak at the source velocity toward the MIR source A/mmA2 suggesting that the emission is originating from closer to the protostar.

astro-ph.SR↗

arXiv2023

A high-resolution radio study of the L1551 IRS 5 and L1551 NE jets

Using observations with e-MERLIN and the VLA, together with archival data from ALMA, we obtain high-resolution radio images of two binary YSOs: L1551 IRS 5 and L1551 NE, covering a wide range of frequencies from 5 - 336 GHz, and resolving emission from the radio jet on scales of only ~15 au. By comparing these observations to those from a previous epoch, it is shown that there is a high degree of variability in the free-free emission from the jets of these sources. In particular, the northern component of L1551 IRS 5 shows a remarkable decline in flux density of a factor of ~5, suggesting that the free-free emission of this source has almost disappeared. By fitting the spectra of the sources, the ionised mass-loss rates of the jets are derived and it is shown that there is significant variability of up to a factor of ~6 on timescales of ~20 years. Using radiative transfer modelling, we also obtained a model image for the jet of the southern component of L1551 IRS 5 to help study the inner region of the ionised high-density jet. The findings favour the X-wind model launched from a very small innermost region.

astro-ph.SR↗

arXiv2023

Water in the terrestrial planet-forming zone of the PDS 70 disk

Terrestrial and sub-Neptune planets are expected to form in the inner ($<10~$AU) regions of protoplanetary disks. Water plays a key role in their formation, although it is yet unclear whether water molecules are formed in-situ or transported from the outer disk. So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks, similar to PDS 70, the first system with direct confirmation of protoplanet presence. Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large ($\sim54~$AU) planet-carved gap separating an inner and outer disk. Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H$_2$, and/or OH, and survival through water self-shielding. This is also supported by the presence of CO$_2$ emission, another molecule sensitive to UV photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir. Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry.

astro-ph.EP↗

arXiv2023

A rich hydrocarbon chemistry and high C to O ratio in the inner disk around a very low-mass star

Carbon is an essential element for life but how much can be delivered to young planets is still an open question. The chemical characterization of planet-forming disks is a crucial step in our understanding of the diversity and habitability of exoplanets. Very low-mass stars ($<0.2~M_{\odot}$) are interesting targets because they host a rich population of terrestrial planets. Here we present the JWST detection of abundant hydrocarbons in the disk of a very low-mass star obtained as part of the MIRI mid-INfrared Disk Survey (MINDS). In addition to very strong and broad emission from C$_2$H$_2$ and its $^{13}$C$^{12}$CH$_2$ isotopologue, C$_4$H$_2$, benzene, and possibly CH$_4$ are identified, but water, PAH and silicate features are weak or absent. The lack of small silicate grains implies that we can look deep down into this disk. These detections testify to an active warm hydrocarbon chemistry with a high C/O ratio in the inner 0.1 au of this disk, perhaps due to destruction of carbonaceous grains. The exceptionally high C$_2$H$_2$/CO$_2$ and C$_2$H$_2$/H$_2$O column density ratios suggest that oxygen is locked up in icy pebbles and planetesimals outside the water iceline. This, in turn, will have significant consequences for the composition of forming exoplanets.

astro-ph.EP↗

arXiv2023

Near-Infrared Polarimetry and H$_2$ emission toward Massive Young Stars: Discovery of a Bipolar Outflow associated to S235 e2s3

We present a near-infrared $H$ band polarimetric study toward the S235 e2s3 protostar, obtained using the POLICAN instrument on the 2.1m OAGH telescope. The images reveal a bipolar outflow with a total length of about 0.5pc. The outflow nebulosity presents a high degree of linear polarization ($\sim80\%$) and reveals a centrosymmetric pattern with the polarization position angles. The polarization characteristics suggest their origin to be single scattering associated with dust in the outflow. Using multiwavelength archival data, we performed spectral energy distribution (SED) fitting based on radiative transfer models of turbulent core accretion theory. The best-fit SED model indicated that the protostar has a mass of $6.8\pm1.2\,M_\odot$, with a disk accretion rate of $3.6\pm1.2\times10^{-4}\,M_\odot\,yr^{-1}$ and a total bolometric luminosity of $9.63\pm2.1\times10^{3}\,L_\odot$. Narrowband H$_2$ ($2.12\,μ$m) observations show shocked emission along the bipolar lobes tracing the jet's interaction with the surrounding medium. The estimated H$_2$ luminosity of the outflow is $2.3_{-1.3}^{+3.5}\,L_\odot$, which matched the known power-law correlation with the source bolometric luminosity, similar to other high-mass outflows. The orientation of the bipolar outflow was found to be parallel to the local magnetic field direction. The overall results assert the fact that the S235 e2s3 source is a massive young star driving a highly collimated bipolar outflow through disk accretion.

astro-ph.SR↗

arXiv2023

High-uniformity TiN/Ti/TiN multilayers for the development of Microwave Kinetic Inductance Detector

Microwave Kinetic Inductance Detectors (MKIDs) are a class of superconducting cryogenic detectors that simultaneously exhibit energy resolution, time resolution and spatial resolution. The pixel yield of MKID arrays is usually a critical figure of merit in the characterisation of an MKIDs array. Currently, for MKIDs intended for the detection of optical and near-infrared photons, only the best arrays exhibit a pixel yield as high as 75-80%. The uniformity of the superconducting film used for the fabrication of MKIDs arrays is often regarded as the main limiting factor to the pixel yield of an array. In this paper we will present data on the uniformity of the TiN/Ti/TiN multilayers deposited at the Tyndall National Institute and compare these results with a statistical model that evaluates how inhomogeneities affect the pixel yield of an array.

astro-ph.IM↗

arXiv2022

V-LoTSS: The Circularly-Polarised LOFAR Two-metre Sky Survey

We present the detection of 68 sources from the most sensitive radio survey in circular polarisation conducted to date. We use the second data release of the 144 MHz LOFAR Two-metre Sky Survey to produce circularly-polarised maps with median 140 $μ$Jy beam$^{-1}$ noise and resolution of 20$''$ for $\approx$27% of the northern sky (5634 deg$^{2}$). The leakage of total intensity into circular polarisation is measured to be $\approx$0.06%, and our survey is complete at flux densities $\geq1$ mJy. A detection is considered reliable when the circularly-polarised fraction exceeds 1%. We find the population of circularly-polarised sources is composed of four distinct classes: stellar systems, pulsars, active galactic nuclei, and sources unidentified in the literature. The stellar systems can be further separated into chromospherically-active stars, M dwarfs, and brown dwarfs. Based on the circularly-polarised fraction and lack of an optical counterpart, we show it is possible to infer whether the unidentified sources are likely unknown pulsars or brown dwarfs. By the completion of this survey of the northern sky, we expect to detect 300$\pm$100 circularly-polarised sources.

astro-ph.GA↗

arXiv2022

Peculiar radio$-$X-ray relationship in active stars

The empirical relationship between the non-thermal 5GHz radio luminosity and the soft X-ray luminosity of active stellar coronae, canonically called the Güdel-Benz relationship (Güdel & Benz 1993), has been a cornerstone of stellar radio astronomy as it explicitly ties the radio emission to the coronal heating mechanisms. The relationship extends from microflares on the Sun to the coronae of the most active stars suggesting that active coronae are heated by a flare-like process (Benz & Güdel 1994). The relationship is thought to originate from a consistent partition of the available flare energy into relativistic charges, that emit in the radio-band via the incoherent gyrosynchrotron mechanism, and heating of the bulk coronal plasma, that emits in the X-ray band via the Bremsstrahlung mechanism. Consequently, coherent emission from stellar and sub-stellar objects is not expected to adhere to this empirical relationship, as is observed in ultracool dwarf stars and brown dwarfs. Here we report a population of radio-detected chromospherically active stars that surprisingly follows the Güdel-Benz relationship despite their radio emission being classified as coherent emission by virtue of its high circularly polarised fraction and high brightness temperature. Our results prompt a re-examination of the physics behind the Güdel-Benz relationship, its implication for the mechanism of coronal heating and particle acceleration in active stars and the phenomenological connection between solar and stellar flares.

astro-ph.SR↗

arXiv2021

First Results from the REAL-time Transient Acquisition backend (REALTA) at the Irish LOFAR station

Modern radio interferometers such as the LOw Frequency ARray (LOFAR) are capable of producing data at hundreds of gigabits to terabits per second. This high data rate makes the analysis of radio data cumbersome and computationally expensive. While high performance computing facilities exist for large national and international facilities, that may not be the case for instruments operated by a single institution or a small consortium. Data rates for next generation radio telescopes are set to eclipse those currently in operation, hence local processing of data will become all the more important. Here, we introduce the REAL-time Transient Acquisition backend (REALTA), a computing backend at the Irish LOFAR station (I-LOFAR) which facilitates the recording of data in near real-time and post-processing. We also present first searches and scientific results of a number of radio phenomena observed by I-LOFAR and REALTA, including pulsars, fast radio bursts (FRBs), rotating radio transients (RRATs), the search for extraterrestrial intelligence (SETI), Jupiter, and the Sun.

astro-ph.IM↗

arXiv2021

A MUSE Spectro-imaging Study of the Th 28 Jet: Precession in the Inner Jet

Context: Th 28 is a Classical T Tauri star in the Lupus 3 cloud which drives an extended bipolar jet. Previous studies of the inner jet identified signatures of rotation around the outflow axis, a key result for theories of jet launching. Thus this is an important source in which to investigate the poorly understood jet launching mechanism. We investigate the morphology and kinematics of the Th 28 micro-jets with the aim of characterizing their structure and outflow activity, using optical integral-field spectroscopy observations obtained with VLT/MUSE. We use spectro-imaging and position-velocity maps to investigate the kinematic and morphological features of the jet, and obtain a catalogue of emission lines in which the jet is visible. A Lucy-Richardson deconvolution procedure is used to differentiate the structure of the inner micro-jet region. Spatial profiles extracted perpendicular to the jet axis are fitted to investigate the jet width, opening angle and the evolution of the jet axis. We confirm the previously identified knot HHW$_{2}$ within the red-shifted jet and identify three additional knots in each lobe for the first time. We also find [O III]$λ$5007 emission from the blue-shifted micro-jet including the knot closest to the star. Proper motions for the innermost knots on each side are estimated and we show that new knots are ejected on an approximate timescale of 10-15 years. The jet axis centroids show a point-symmetric wiggle within the inner portion of both micro-jets indicating precession. We use the jet shape to measure a precession period of 8 years, with a half-opening angle < 0.6$^{\circ}$. This may provide an alternative explanation for the rotation signatures previously reported. We find the jet shape to be compatible with precession due to a brown dwarf companion orbiting at a separation $\leq$ 0.3 au.

astro-ph.SR↗

arXiv2021

Detection of coherent low-frequency radio bursts from weak-line TTauri stars

In recent years, thanks to new facilities such as LOFAR capable of sensitive observations, much work has been done on the detection of stellar radio emission at low frequencies. Such emission has commonly been shown to be coherent emission, generally attributed to electron-cyclotron maser emission, and has usually been detected from main-sequence M dwarfs. Here we report the first detection of coherent emission at low frequencies from T Tauri stars, which are known to be associated with high levels of stellar activity. Using LOFAR, we have detected several bright radio bursts at 150 MHz from two weak-line T Tauri stars: KPNO-Tau 14 and LkCa 4. All of the bursts have high brightness temperatures ($10^{13} - 10^{14}\ \mathrm{K}$) and high circular polarization fractions (60 - 90 \%), indicating that they must be due to a coherent emission mechanism. This could be either plasma emission or electron-cyclotron maser (ECM) emission. Due to the exceptionally high brightness temperatures seen in at least one of the bursts ($\geq 10^{14}\ \mathrm{K}$), and the high circular polarization levels, it seems unlikely that plasma emission could be the source and so ECM is favoured as the most likely emission mechanism. Assuming this is the case, the required magnetic field in the emission regions would be 40 - 70 G. We determine that the most likely method of generating ECM emission is plasma co-rotation breakdown in the stellar magnetosphere. There remains the possibility, however, it could be due to an interaction with an orbiting exoplanet.

astro-ph.SR↗

arXiv2021

Large closed-field corona of WX UMa evidenced from radio observations

The space-weather conditions that result from stellar winds significantly impact the habitability of exoplanets. The conditions can be calculated from first principles if the necessary boundary conditions -- namely on the plasma density in the outer corona and the radial distance at which the plasma forces the closed magnetic field into an open geometry -- are specified. Low frequency radio observations ($ν\lesssim 200$ MHz) of plasma and cyclotron emission from stars probe these magneto-ionic conditions. Here we report the detection of low-frequency ($120-167\,{\rm MHz}$) radio emission associated with the dMe6 star WX UMa. If the emission originates in WX UMa's corona, we show that the closed field regions extends to at least $\approx 10$ stellar radii, that is about a factor of a few larger than the solar value, and possibly to $\gtrsim 20$ stellar radii. Our results suggest that the magnetic-field structure of M dwarfs is in between Sun-like and planet-like configurations, where compact over-dense coronal loops with X-ray emitting plasma co-exist with a large-scale magnetosphere with lower plasma density and closed magnetic geometry.

astro-ph.SR↗

arXiv2021

A measure of the size of the magnetospheric accretion region in TW Hydrae

Stars form by accreting material from their surrounding disks. There is a consensus that matter flowing through the disk is channelled onto the stellar surface by the stellar magnetic field. This is thought to be strong enough to truncate the disk close to the so-called corotation radius where the disk rotates at the same rate as the star. Spectro-interferometric studies in young stellar objects show that Hydrogen is mostly emitted in a region of a few milliarcseconds across, usually located within the dust sublimation radius. Its origin is still a matter of debate and it can be interpreted as coming from the stellar magnetosphere, a rotating wind or a disk. In the case of intermediate-mass Herbig AeBe stars, the fact that the Br gamma emission is spatially resolved rules out that most of the emission comes from the magnetosphere. This is due to the weak magnetic fields (some tenths of G) detected in these sources, resulting in very compact magnetospheres. In the case of T Tauri sources, their larger magnetospheres should make them easier to resolve. However, the small angular size of the magnetosphere (a few tenths of milliarcseconds), along with the presence of winds emitting in Hydrogen make the observations interpretation challenging. Here, we present direct evidence of magnetospheric accretion by spatially resolving the inner disk of the 60 pc T Tauri star TW Hydrae through optical long baseline interferometry. We find that the hydrogen near-infrared emission comes from a region approximately 3.5 stellar radii (R*) across. This region is within the continuum dusty disk emitting region (Rcont = 7 R*) and smaller than the corotation radius which is twice as big. This indicates that the hydrogen emission originates at the accretion columns, as expected in magnetospheric accretion models, rather than in a wind emitted at much larger distance (>1au).

astro-ph.SR↗

arXiv2021

Magnetic fields and Star Formation around HII regions: The S235 complex

Magnetic fields are ubiquitous and essential in star formation. In particular, their role in regulating formation of stars across diverse environments like HII regions needs to be well understood. In this study, we present magnetic field properties towards the S235 complex using near-infrared (NIR) $H$-band polarimetric observations, obtained with the Mimir and POLICAN instruments. We selected 375 background stars in the field through combination of Gaia distances and extinctions from NIR colors. The plane-of-sky (POS) magnetic field orientations inferred from starlight polarization angles reveal a curved morphology tracing the spherical shell of the HII region. The large-scale magnetic field traced by Planck is parallel to the Galactic plane. We identified 11 dense clumps using $1.1\,\mathrm{mm}$ dust emission, with masses between $33-525\,\rm M_\odot$. The clump averaged POS magnetic field strengths were estimated to be between $36-121\,\mathrm{μG}$, with a mean of ${\sim}65\,\mathrm{μG}$. The mass-to-flux ratios for the clumps are found to be sub-critical with turbulent Alfvén Mach numbers less than 1, indicating a strongly magnetized region. The clumps show scaling of magnetic field strength vs density with a power-law index of $0.52\pm0.07$, similar to ambipolar diffusion models. Our results indicate the S235 complex is a region where stellar feedback triggers new stars and the magnetic fields regulate the rate of new star formation.

astro-ph.GA↗

arXiv2021

Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission

Recently detected coherent low-frequency radio emission from M dwarf systems shares phenomenological similarities with emission produced by magnetospheric processes from the gas giant planets of our Solar System. Such beamed electron-cyclotron maser emission can be driven by a star-planet interaction or a breakdown in co-rotation between a rotating plasma disk and a stellar magnetosphere. Both models suggest that the radio emission could be periodic. Here we present the longest low-frequency interferometric monitoring campaign of an M dwarf system, composed of twenty-one $\approx$8 hour epochs taken in two series of observing blocks separated by a year. We achieved a total on-source time of 6.5 days. We show that the M dwarf binary CR Draconis has a low-frequency 3$σ$ detection rate of 90$^{+5}_{-8}$% when a noise floor of $\approx$0.1 mJy is reached, with a median flux density of 0.92 mJy, consistent circularly polarised handedness, and a median circularly polarised fraction of 66%. We resolve three bright radio bursts in dynamic spectra, revealing the brightest is elliptically polarised, confined to 4 MHz of bandwidth centred on 170 MHz, and reaches a flux density of 205 mJy. The burst structure is mottled, indicating it consists of unresolved sub-bursts. Such a structure shares a striking resemblance with the low-frequency emission from Jupiter. We suggest the near-constant detection of high brightness temperature, highly-circularly-polarised radiation that has a consistent circular polarisation handedness implies the emission is produced via the electron-cyclotron maser instability. Optical photometric data reveal the system has a rotation period of 1.984$\pm$0.003 days. We observe no periodicity in the radio data, but the sampling of our radio observations produces a window function that would hide the near two-day signal.

astro-ph.SR↗