Bright Mid-infrared Source Research Articles

A low-cost chopping system and uncooled microbolometer array for ground-based astronomy

Mid-Infrared imaging is vital for the study of a wide variety of astronomical phenomena, including evolved stars, exoplanets, and dust enshrouded processes such as star formation in galaxies. However, infrared detectors have traditionally been expensive and it is difficult to achieve the sensitivity needed to see beyond the overwhelming mid-infrared background. Here we describe the upgrade and commissioning of a simple prototype, low-cost 10 μ m imaging instrument. The system was built using commercially available components including an uncooled microbolometer focal plane array and chopping system. The system was deployed for a week on the 1.52 m Carlos Sanchez Telescope and used to observe several very bright mid-infrared sources with catalogue fluxes down to sim 600 Jy. We report a sensitivity improvement of sim 4 mag over our previous unchopped observations, in line with our earlier predictions.

Mitigating fringing in discrete frequency infrared imaging using time-delayed integration.

Infrared (IR) spectroscopic microscopes provide the potential for label-free quantitative molecular imaging of biological samples, which can be used to aid in histology, forensics, and pharmaceutical analysis. Most IR imaging systems use broadband illumination combined with a spectrometer to separate the signal into spectral components. This technique is currently too slow for many biomedical applications such as clinical diagnosis, primarily due to the availability of bright mid-infrared sources and sensitive MCT detectors. There has been a recent push to increase throughput using coherent light sources, such as synchrotron radiation and quantum cascade lasers. While these sources provide a significant increase in intensity, the coherence introduces fringing artifacts in the final image. We demonstrate that applying time-delayed integration in one dimension can dramatically reduce fringing artifacts with minimal alterations to the standard infrared imaging pipeline. The proposed technique also offers the potential for less expensive focal plane array detectors, since linear arrays can be more readily incorporated into the proposed framework.

Massive envelopes and filaments in the NGC 3603 star forming region

The formation of massive stars and their arrival on the zero-age main-sequence occurs hidden behind dense clouds of gas and dust. In the giant Hii region NGC 3603, the radiation of a young cluster of OB stars has dispersed dust and gas in its vicinity. At a projected distance of 2:5 pc from the cluster, a bright mid-infrared (mid-IR) source (IRS 9A) had been identified as a massive young stellar object (MYSO), located on the side of a molecular clump (MM2) of gas facing the cluster. We investigated the physical conditions in MM2, based on APEX sub-mm observations using the SABOCA and SHFI instruments, and archival ATCA 3 mm continuum and CS spectral line data. We resolved MM2 into several compact cores, one of them closely associated with IRS 9A. These are likely infrared dark clouds as they do not show the typical hot-core emission lines and are mostly opaque against the mid-IR background. The compact cores have masses of up to several hundred times the solar mass and gas temperatures of about 50 K, without evidence of internal ionizing sources. We speculate that IRS 9A is younger than the cluster stars, but is in an evolutionary state after that of the compact cores.

Breath Analysis with Broadly Tunable Quantum Cascade Lasers

With the availability of broadly tunable external cavity quantum cascade lasers (EC-QCLs), particularly bright mid-infrared (MIR; 3-20 μm) light sources are available offering high spectral brightness along with an analytically relevant spectral tuning range of >2 μm. Accurate isotope ratio determination of (12)CO2 and (13)CO2 in exhaled breath is of critical importance in the field of breath analysis, which may be addressed via measurements in the MIR spectral regime. Here, we combine for the first time an EC-QCL tunable across the (12)CO2/(13)CO2 spectral band with a miniaturized hollow waveguide gas cell for quantitatively determining the (12)CO2/(13)CO2 ratio within the exhaled breath of mice. Due to partially overlapping spectral features, these studies are augmented by appropriate multivariate data evaluation and calibration techniques based on partial least-squares regression along with optimized data preprocessing. Highly accurate determinations of the isotope ratio within breath samples collected from a mouse intensive care unit validated via hyphenated gas chromatography-mass spectrometry confirm the viability of IR-HWG-EC-QCL sensing techniques for isotope-selective exhaled breath analysis.

FOUR DECADES OF IRC +10216: EVOLUTION OF A CARBON-RICH DUST SHELL RESOLVED AT 10 μm WITH MMT ADAPTIVE OPTICS AND MIRAC4,,

The evolved carbon-rich AGB star IRC +10216 (CW Leo) is the brightest mid-infrared source outside the solar system, as well as one of the closest examples of an evolved star losing mass. It has a complex and variable circumstellar structure on small scales in the near-IR, and mid-IR interferometry has revealed a dynamic dust formation zone. We have obtained diffraction limited imaging and grism spectroscopy of IRC +10216 at the 6.5m MMT in the N-band (~8-13 microns). These new observations show that a change has occurred in the dust shell surrounding IRC +10216 over the last two decades, which is illustrated by a change in the apparent shape of the well known SiC spectral feature at ~11 microns and a reduction in the continuum at 13 microns. As expected, our diffraction limited spatial information shows an extended circumstellar envelope. We also demonstrate that the dusty envelope appears to be ~30% larger at the wavelengths of the SiC feature, likely due to the increased opacity of SiC. The deconvolved FWHM of the object increases from 0.43" (~56 AU) for wavelength < 10 microns to 0.58" (~75 AU) at 11.8 microns, then decreases to 0.5" (~65 AU) at 12.7 microns. Our estimates of IRC +10216's size allow us to plausibly tie the change in the spectrum over the last 12.5 years to the evolution of the dusty circumstellar envelope at speeds of 12-17 km/sec.

A double detached shell around a post-red supergiant: IRAS 17163-3907, the Fried Egg nebula

We performed a mid-infrared imaging survey of evolved stars in order to study the dust distribution in circumstellar envelopes around these objects and to better understand the mass-loss mechanism responsible for the formation of these envelopes. During this survey, we resolved for the first time the circumstellar environment of IRAS 17163-3907 (hereinafter IRAS17163), which is one of the brightest objects in the mid-infrared sky, but is surprisingly not well studied. Our aim is to determine the evolutionary status of IRAS 17163 and study its circumstellar environment in order to understand its mass-loss history. We obtained diffraction-limited images of IRAS 17163 in the mid-infrared using VISIR on the VLT. Optical spectra of the object allowed us to determine its spectral type and estimate its distance via the presence of diffuse interstellar bands. We show that IRAS 17163 is a Post-Red Supergiant, possibly belonging to the rare class of Yellow Hypergiants, and is very similar to the well studied object IRC +10420. Our mid-infrared images of IRAS 17163 are the first direct images of this bright mid-infrared source. These images clearly show the presence of a double dusty detached shell around the central star, due to successive ejections of material with a timescale of the order of 400 years and a total circumstellar mass larger than 4 M$_{\odot}$. This indicates that non quiescent mass-loss occurs during this phase of stellar evolution.

Chandra Stacking Constraints on the Contribution of 24 μm Spitzer Sources to the Unresolved Cosmic X-Ray Background

We employ X-ray stacking techniques to examine the contribution from X-ray-undetected, mid-infrared-selected sources to the unresolved, hard (6-8 keV) cosmic X-ray background (CXB). We use the publicly available, 24 μm Spitzer Space Telescope MIPS catalogs from the Great Observatories Origins Deep Survey (GOODS)-North and South fields, which are centered on the 2 Ms Chandra Deep Field-North and 1 Ms Chandra Deep Field-South, to identify bright (S24 μm > 80 μJy) mid-infrared sources that may be powered by heavily obscured AGNs. We measure a significant stacked X-ray signal in all of the X-ray bands examined, including, for the first time, a significant (3.2 σ) 6-8 keV stacked X-ray signal from an individually undetected X-ray source population. We find that the X-ray-undetected MIPS sources make up ≈2% (or less) of the total CXB below 6 keV, but ≈6% in the 6-8 keV band. The 0.5-8 keV stacked spectrum is consistent with a hard power law (Γ = 1.44 ± 0.07), with the spectrum hardening at higher X-ray energies. Our findings show that these bright MIPS sources do contain obscured AGNs, but are not the primary source of the unresolved ~40% of 6-8 keV CXB. Our study rules out obscured, luminous quasars as a significant source of the remaining unresolved CXB and suggests that it most likely arises from a large population of obscured, high-redshift (z 1), Seyfert-luminosity AGNs.

Clustered Star Formation in the Small Magellanic Cloud. ASpitzer/IRAC View of the Star‐Forming Region NGC 602/N 90

We present Spitzer/IRAC photometry on the star-forming HII region N 90, related to the young stellar association NGC 602 in the Small Magellanic Cloud. Our photometry revealed bright mid-infrared sources, which we classify with the use of a scheme based on templates and models of red sources in the Milky Way, and criteria recently developed from the Spitzer Survey of the SMC for the selection of candidate Young Stellar Objects (YSOs). We detected 57 sources in all four IRAC channels in a 6.2' x 4.8' field-of-view centered on N 90; 22 of these sources are classified as candidate YSOs. We compare the locations of these objects with the position of optical sources recently found in the same region with high-resolution HST/ACS imaging of NGC 602, and we find that 17 candidate YSOs have one or more optical counterparts. All of these optical sources are identified as pre-main sequence stars, indicating, thus, ongoing clustered star formation events in the region. The positions of the detected YSOs and their related PMS clusters give a clear picture of the current star formation in N 90, according to which the young stellar association photo-ionizes the surrounding interstellar medium, revealing the HII nebula, and triggering sequential star formation events mainly along the eastern and southern rims of the formed cavity of the parental molecular cloud.

TheSpitzerSurvey of the Small Magellanic Cloud: S3MC Imaging and Photometry in the Mid‐ and Far‐Infrared Wave Bands

We present the initial results from the Spitzer Survey of the Small Magellanic Cloud (S3MC), which imaged the star-forming body of the Small Magellanic Cloud (SMC) in all seven MIPS and IRAC wavebands. We find that the F_8/F_24 ratio (an estimate of PAH abundance) has large spatial variations and takes a wide range of values that are unrelated to metallicity but anticorrelated with 24 um brightness and F_24/F_70 ratio. This suggests that photodestruction is primarily responsible for the low abundance of PAHs observed in star-forming low-metallicity galaxies. We use the S3MC images to compile a photometric catalog of ~400,000 mid- and far-infrared point sources in the SMC. The sources detected at the longest wavelengths fall into four main categories: 1) bright 5.8 um sources with very faint optical counterparts and very red mid-infrared colors ([5.8]-[8.0]>1.2), which we identify as YSOs. 2) Bright mid-infrared sources with mildly red colors (0.16<[5.8]-[8.0]<0.6), identified as carbon stars. 3) Bright mid-infrared sources with neutral colors and bright optical counterparts, corresponding to oxygen-rich evolved stars. And, 4) unreddened early B stars (B3 to O9) with a large 24 um excess. This excess is reminiscent of debris disks, and is detected in only a small fraction of these stars (<5%). The majority of the brightest infrared point sources in the SMC fall into groups one to three. We use this photometric information to produce a catalog of 282 bright YSOs in the SMC with a very low level of contamination (~7%).

Mid‐Infrared High Spatial Resolution Observations of NGC 1569: Detection of Embedded Embryos of Star Formation

We present high spatial resolution mid-infrared (MIR) imaging and spectroscopic observations of the dwarf galaxy NGC 1569 with COMICS on the Subaru telescope. The [S IV] 10.5 μm image clearly shows four pointlike sources and one extended source together with the diffuse emission. The brightest MIR source (MIR1) coincides with the intense H II region, which does not have a corresponding optical source and should thus be a source embedded in dust clouds. The infrared luminosity suggests that there are about 40 O7 stars associated with MIR1. The second brightest source located ~15 south of MIR1 (MIR2) is detected for the first time. This source is not seen in the radio continuum. These characteristics can be accounted for if ionizing regions in the source are compact and optically thick in the radio. The large infrared luminosity (~2 × 108 L☉) suggests that there are about 950 O7 stars in MIR2 and significant contributions from sources other than O-type stars, such as less massive stars and/or pre-main-sequence stars. If this interpretation is correct, MIR2 could be in a very early phase of massive star formation. The unidentified infrared (UIR) band at 11.2 μm is also detected in the spectrum of MIR2. The strength of the UIR band decreases with the [S IV] emission, suggesting that the UIR band weakens and the band carriers are destroyed in strong radiation fields. Super star cluster (SSC) A is also detected in the N-band images. The mid-infrared characteristics support the difference in the ages between two components of SSC A.

Revealing the environs of the remarkable southern hot core G327.3–0.6

Aims. We present a submm study of the massive hot core G327.3-0.6 that constrains its physical parameters and environment. Methods. The APEX telescope was used to image CO and $\mathrm{N_2H^+}$ emission, to observe lines from other molecules toward a hot and a cold molecular core, and to measure the continuum flux density of the hot core. Results. In the $\mathrm{C^{18}O}$ $J=3 {-} 2$ line, two clumps were found, one associated with the Hii region G327.3-0.5 and the other associated with the hot core. An additional cold clump is found 30´´ (0.4 pc) northeast of the hot core in bright $\mathrm{N_2H^+}$ emission. From the the continuum data, we calculate a mass of 420 $M_\odot$ and a size of 0.1 pc for the hot core. A new, more accurate position of the hot core is reported, which allows the association of the core with a bright mid-infrared source. The luminosity of the hot core is estimated to be between 5 and $15\times 10^4$ $L_\odot$. Conclusions. This study revealed several different evolutionary stages of massive star formation in the G327.3-0.6 region.

Isolated, Massive Supergiants near the Galactic Center

We have carried out a pilot project to assess the feasibility of using radio, infrared, and X-ray emission to identify young, massive stars located between 1 and 25 pc from the Galactic center. We first compared catalogs compiled from the VLA, Chandra, and 2MASS. We identified two massive, young stars: the previously identified star that is associated with the radio H II region H2 and a newly identified star that we refer to as CXOGC J174516.1-290315. The infrared spectra of both stars exhibit very strong Brγ and He I lines and resemble those of massive supergiants that have evolved off of the main sequence but not yet reached the Wolf-Rayet phase. We estimate that each star has a bolometric luminosity 106 L☉. These two stars are also associated with bright mid-infrared sources from the MSX survey, although the origin of this emission is uncertain. Likewise, the detection of these two sources in X-rays is surprising because stars at similar evolutionary states are not uniformly bright X-ray sources. Therefore, we suggest that both stars are in binary systems that contain either OB stars whose winds collide with those of the luminous supergiants or compact objects that are accreting from the winds of the supergiants. We also identify X-ray emission from a nitrogen-type Wolf-Rayet star and place upper limits on the X-ray luminosities of three more evolved, massive stars that previously have been identified between 1 and 25 pc from Sgr A*. Finally, we briefly discuss the implications that future searches for young stars will have for our understanding of the recent history of star formation near the Galactic center.

Mid-infrared imaging of a young bipolar nebula in the S287 molecular cloud

We present diffraction-limited images in the 11.3 μm PAH band and in the continuum at 11.9 μm of the S287B star forming region obtained with the newly commissioned mid-infrared imager/spectrometer VISIR at the VLT. In both filters five point-like sources are detected, of which at least one has a spectral energy distribution reminiscent of a Lada Class I source. We also report on the discovery of a new Herbig Ac star in this region. It is particularly striking that the brightest mid-infrared source in this region has not been detected at shorter wavelengths; it is a good candidate to be the driving source of the bipolar molecular outflow and optical reflection nebulosity previously reported in S287B.

Discovery of a Large ∼200 kpc Gaseous Nebula atz≈ 2.7 with theSpitzer Space Telescope

We report the discovery of a very large, spatially extended Lyα-emitting nebula at z = 2.656 associated with a luminous mid-infrared source. The bright mid-infrared source (F24 μm = 0.86 mJy) was first detected in observations made using the Spitzer Space Telescope. Existing broadband imaging data from the NOAO Deep Wide-Field Survey revealed the mid-infrared source to be associated with a diffuse, spatially extended, optical counterpart in the BW band. Spectroscopy and further imaging of this target reveals that the optical source is an almost purely line-emitting nebula with little, if any, detectable diffuse continuum emission. The Lyα nebula has a luminosity of LLyα ≈ 1.7 × 1044 ergs s-1 and an extent of at least 20'' (160 kpc). Its central ≈8'' shows an ordered, monotonic velocity profile; interpreted as rotation, this region encloses a mass M ≈ 6 × 1012 M☉. Several sources lie within the nebula. The central region of the nebula shows narrow (≈365 km s-1) emission lines of C IV and He II. The mid-infrared source is a compact object lying within the nebula but offset from the center by a projected distance of ≈25 (20 kpc), and likely to be an enshrouded AGN. A young star-forming galaxy lies near the northern end of the nebula. We suggest that the nebula is a site of recent multiple galaxy and AGN formation, with the spatial distribution of galaxies within the nebula perhaps tracking the formation history of the system.

Subarcsecond mid-infrared and radio observations of the W3 IRS5 protocluster

Observations at mid-infrared (4.8-17.65 μm) and radio (0.7-1.3 cm) wavelengths are used to constrain the structure of the high-mass star-forming region W3 IRS5 on 0.1 (200 AU) scales. Two bright mid-infrared sources are detected, as well as diffuse emission. The bright sources have associated compact radio emission and probably are young high-mass stars. The measured sizes and estimated temperatures indicate that these sources together can supply the observed far-infrared luminosity. However, an optically thick radio source with a possible mid-infrared counterpart may also contribute significant luminosity; if so, it must be extremely deeply embedded. The infrared colour temperatures of 350-390 K and low radio brightness suggest gravitational confinement of the H II regions and ongoing accretion at a rate of a few 10 -8 M ○. yr -1 or more. Variations in the accretion rate would explain the observed radio variability. The low estimated foreground extinction suggests the existence of a cavity around the central stars, perhaps blown by stellar winds. At least three radio sources without mid-infrared counterparts appear to show proper motions of ∼100 km s -1 , and may be deeply embedded young runaway OB stars, but more likely are clumps in the ambient material which are shock-ionized by the OB star winds.

The 3.28 micron emission feature in NGC 253

view Abstract Citations (25) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The 3.28 Micron Emission Feature in NGC 253 Kalas, Paul ; Wynn-Williams, C. G. Abstract The 3.28 micron polycyclic aromatic hydrocarbon (PAH) emission feature in the galaxy NGC 253 comes from an extended star formation region ~100 pc across. The brightest mid-infrared source in the galaxy, which is displaced ~45 pc from the probable nucleus, does not show the PAH feature; it may be a dust-enshrouded recent supernova. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174756 Bibcode: 1994ApJ...434..546K Keywords: Emission Spectra; Infrared Astronomy; Polycyclic Aromatic Hydrocarbons; Spiral Galaxies; Star Formation; Supernovae; Active Galactic Nuclei; Infrared Astronomy Satellite; Infrared Imagery; Luminosity; Astronomy; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 253; GALAXIES: ISM; GALAXIES: NUCLEI full text sources ADS | data products SIMBAD (7) NED (1)

NGC 2024 - Far-infrared and radio molecular observations

New far-infrared continuum and millimeter-wave molecular observations of NGC 2024 are presented. The measurements were obtained at relatively high angular resolution making it possible to describe the source energetics and mass distribution in greater detail than previously reported. The object appears to be dominated by a dense ridge of material, extended in the north-south direction and centered on the dark lane that is seen in visual photographs. The maps of the source using the 'high-density' molecules CS and HCN confirm this picture and makes it possible to describe the core structure and molecular abundances. The radio molecular and infrared observations support the idea that an important exciting star in NGC 2024 has yet to be identified and is centered on the dense ridge about 1 arcmin south of the bright mid-infrared source IRS 2. The data presented here, along with other observations, make it possible to describe a model for the source.