J. A. Acosta-Pulido

The Formation of Fullerenes: Clues from New C60, C70, and (Possible) Planar C24 Detections in Magellanic Cloud Planetary Nebulae

We present 10 new Spitzer detections of fullerenes in Magellanic Cloud Planetary Nebulae, including the first extragalactic detections of the C70 molecule. These new fullerene detections together with the most recent laboratory data permit us to report an accurate determination of the C60 and C70 abundances in space. Also, we report evidence for the possible detection of planar C24 in some of our fullerene sources, as indicated by the detection of very unusual emission features coincident with the strongest transitions of this molecule at ~6.6, 9.8, and 20 μm. The infrared spectra display a complex mix of aliphatic and aromatic species such as hydrogenated amorphous carbon grains (HACs), polycyclic aromatic hydrocarbon clusters, fullerenes, and small dehydrogenated carbon clusters (possible planar C24). The coexistence of such a variety of molecular species supports the idea that fullerenes are formed from the decomposition of HACs. We propose that fullerenes are formed from the destruction of HACs, possibly as a consequence of shocks driven by the fast stellar winds, which can sometimes be very strong in transition sources and young planetary nebulae (PNe). This is supported by the fact that many of our fullerene-detected PNe show altered [Ne III]/[Ne II] ratios suggestive of shocks as well as P-Cygni profiles in their UV lines indicative of recently enhanced mass loss.

The outburst and nature of two young eruptive stars in the North America/Pelican Nebula Complex

Context. In August 2010, the sudden optical brightening of two young stellar objects, HBC 722 and VSX J205126.1+440523, located in the North America/Pelican Nebula Complex, was announced. Early photometric and spectroscopic observations of these objects indicated that they may belong to the FUor or EXor class of young eruptive stars. The eruptions of FUors and EXors are often ex- plained by enhanced accretion of material from the circumstellar disk to the protostar. Aims. In order to determine the true nature of these two objects, we started an optical and near-infrared monitoring program, a nd complemented our data with archival observations and data from the literature. Methods. We plot and analyze pre-outburst and outburst spectral energy distributions (SEDs), multi-filter light curves, and col or-color diagrams. Results. The quiescent SED of HBC 722 is consistent with that of a slightly reddened normal T Tauri-type star. The source bright- ened monotonically in about two months, and the SED obtained during maximum brightness indicates the appearance of a hot, single-temperature blackbody. The current fading rate implies that the star will return to quiescence in about a year, q uestioning its classification as a bone fide FUor. The quiescent SED of VSX J20 5126.1+440523 looks like that of a highly embedded Class I source. The outburst of this source happened more gradually, but reached an unprecedentedly high amplitude. At 2.5 months after the peak, its light curves show a deep minimum, when the object was close to its pre-outburst optical brightness. Further monitori ng indicates that it is still far from being quiescent. Conclusions. The shape of the light curves, as well as the bolometric luminosities and accretion rates suggest that these objects do no t fit into the classic FUor group. Although HBC 722 exhibit all s pectral characteristics of a bona fide FUor, its luminosity a nd accretion rate is too low, and its timescale is too fast compared to clas sical FUors. VSX J205126.1+440523 seems to be an example where quick extinction changes modulate the light curve.

The awakening of BL Lacertae: observations by Fermi, Swift and the GASP-WEBT

Since the launch of the Fermi satellite, BL Lacertae has been moderately active at ?-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST–AGILE Support Program of the Whole Earth Blazar Telescope in collaboration with the Steward Observatory allows us to perform a detailed comparison with the daily ?-ray observations by Fermi. Discrete correlation analysis between the optical and ?-ray emission reveals correlation with a time lag of 0 ± 1 d, which suggests cospatiality of the corresponding jet emitting regions. A better definition of the time lag is hindered by the daily gaps in the sampling of the extremely fast flux variations. In general, optical flares present more structure and develop on longer time-scales than corresponding ?-ray flares. Observations at X-rays and at millimetre wavelengths reveal a common trend, which suggests that the region producing the mm and X-ray radiation is located downstream from the optical and ?-ray-emitting zone in the jet. The mean optical degree of polarization slightly decreases over the considered period and in general it is higher when the flux is lower. The optical electric vector polarization angle (EVPA) shows a preferred orientation of about 15°, nearly aligned with the radio core EVPA and mean jet direction. Oscillations around it increase during the 2011–2012 outburst. We investigate the effects of a geometrical interpretation of the long-term flux variability on the polarization. A helical magnetic field model predicts an evolution of the mean polarization that is in reasonable agreement with the observations. These can be fully explained by introducing slight variations in the compression factor in a transverse shock waves model.

THE STRUCTURE OF THE ACCRETION DISK IN THE LENSED QUASAR SBS 0909+532

We derive the size and temperature profile of the accretion disk of the lensed quasar SBS 0909+532 by measuring the wavelength dependence (chromaticity) of the microlensing magnification produced by the stars in the lens galaxy. After correcting for extinction using the flux ratios of 14 emission lines, we observe a marked change in the B-A flux ratio with wavelength, varying from –0.67 ± 0.05 mag at (rest frame) ~1460 A to –0.24 ± 0.07 mag at ~6560 A. For λ 7000 A both effects, extinction and microlensing, look minimal. Simulations indicate that image B rather than A is strongly microlensed. If we model the change in disk size from 1460 A to 6560 A using a Gaussian source (I ∝ exp(–R 2/2r 2 s )) with a disk size scaling with wavelength as rs ∝ λ p , we find rs = 7+5 –3 light-days at 1460 A and p = 0.9+0.6 –0.3 for uniform priors on rs and p, and rs = 4+3 –3 light-days and p = 1.0+0.6 –0.4 for a logarithmic prior on rs . The disk temperature profile T ∝ R –1/p is consistent with thin disk theory (T ∝ R –3/4), given the uncertainties. The estimates of rs are also in agreement with the size inferred from thin disk theory using the estimated black hole mass (M BH 2 × 109 M ☉) but not with the smaller size estimated from thin disk theory and the optical flux. We also use the flux ratios of the unmicrolensed emission lines to determine the extinction curve of the dust in the lens galaxy, finding that it is similar to that of the LMC2 Supershell.

Probing the nuclear and circumnuclear activity of NGC 1365 in the infrared

This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy) and CICYT/MCYT (Spain). SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA).

Age and metallicity gradients support hierarchical formation for M87

In order to probe the inside-out formation of the most massive galaxies in the Universe, we have explored the radial (0.1 < R < 8 kpc) variation of the spectral energy distribution (SED) of M87 from UV to IR. For this purpose, we have combined high resolution data in 16 different bands. Our analysis indicate that the age of the stellar population of M87 remains almost unchanged with radius. However, the metallicity ([Z/H]) profile presents three different zones: the innermost kpc shows a plateau with supersolar metallicity, followed by a decline in metallicity down to 5 kpc and another plateau afterwards. The size of the inner plateau is similar to the expected size (Re) of an object with the predicted mass of M87 at z=2. The global [Z/H] gradient is -0.26 +- 0.10, similar to those found in other nearby massive ellipticals. The observed change in the stellar population of M87 is consistent with a rapid formation of the central part (R<5 kpc) of this galaxy followed by the accretion of the outer regions through the infall of more metal-poor material.

Nuclear obscuration in LINERs

Context. Most of the optically classified low-ionisation, narrow emission-line regions (LINERs) nuclei host an active galactic nucleus (AGN). However, how they fit into the unified model (UM) of AGN is still an open question. Aims. The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e. hydrogen column densities of NH > 1:5 10 24 cm 2 ) and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. Methods. We have compiled all the available low spectral-resolution, mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PG QSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and StarBurst (SB) nuclei. We studied the AGN compared to the starburst content in our sample using di erent indicators: the equivalent width of the polycyclic aromatic hydrocarbon at 6.2 m, the strength of the silicate feature at 9.7 m, and the steepness of the mid-IR spectra. We classified the spectra as SB-dominated and AGN-dominated, according to these diagnostics and compared the average mid-IR spectra of the various classes. Moreover, we studied the correlation between the 12 m luminosity, L (12 m), and the 2 10 keV energy band X-ray luminosity, LX(2 10 keV). Results. In 25 out of the 40 LINERs (i.e. 62.5%), the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is di erent from the average spectra of the other optical classes, showing a rather flat spectrum at 6 28 m. We find that the average spectrum of AGN-dominated LINERs with X-ray luminosities LX(2 10 keV) > 10 41 erg/s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. LX(2 10 keV) < 10 41 erg/s) show flat spectra di erent from any of the other optical classes. The correlation between L (12 m) and LX(2 10 keV) for AGN nicely extends towards low luminosities only if SB-dominated LINERs are excluded and if the 2 10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. Conclusions. We find that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence that the dusty-torus disappear when their bolometric luminosity is below Lbol ’ 10 42 erg/s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. To reconcile the Compton-thick nature of a large number of LINERs without dusty-torus signatures, we suggest that the material producing the Compton-thick X-ray obscuration is free of dust.Context. Most of the optically classified low ionisation narrow emission-line regions (LINERs) nuclei host an active galactic nuclei (AGN). However, how they fit into the unified model (UM) of AGN is still an open question. Aims. The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e hydrogen column densities of NH > 1:5 10 24 cm 2 ); and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. Methods. We have compiled all the available low spectral resolution mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PG QSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and Starburst (SBs) nuclei. We have studied the AGN versus the starburst content in our sample using di erent indicators: the equivalent width (EW) of the polycyclic aromatic hydrocarbon (PAH) at 6:2 m, the strength of the silicate feature at 9.7 m, and the steepness of the mid-IR spectra. We have classified the spectra as SB-dominated and AGNdominated, according to these diagnostics. We have compared the average mid-IR spectra of the various classes. Moreover, we have studied the correlation between the 12 m luminosity, L (12 m), and the 2-10 keV energy band X-ray luminosity, LX(2 10 keV). Results. In 25 out of the 40 LINERs (i.e., 62.5%) the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is di erent from the average spectra of the other optical classes, showing a rather flat spectrum at 6 28 m. We have found that the average spectrum of AGN-dominated LINERs with X-ray luminosities LX(2 10 keV) > 10 41 erg=s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. LX(2 10 keV) < 10 41 erg=s) show flat spectra di erent from any of the other optical classes. The correlation between L (12 m) and LX(2 10 keV) for AGN nicely extends toward low luminosities only if SB-dominated LINERs are excluded and the 2-10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. Conclusions. We have found that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence in favour of the dusty-torus disappearance when their bolometric luminosity is below Lbol’ 10 42 erg=s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. In order to reconcile the Compton-thick nature of a large fraction of LINERs with the lack of dusty-torus signatures, we suggest that the material producing the Compton-thick X-ray obscuration is free of dust.

Nuclear obscuration in LINERs - Clues from Spitzer/IRS spectra on the Compton thickness and the existence of the dusty torus

Context. Most of the optically classified low-ionisation, narrow emission-line regions (LINERs) nuclei host an active galactic nucleus (AGN). However, how they fit into the unified model (UM) of AGN is still an open question. Aims. The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e. hydrogen column densities of NH > 1:5 10 24 cm 2 ) and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. Methods. We have compiled all the available low spectral-resolution, mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PG QSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and StarBurst (SB) nuclei. We studied the AGN compared to the starburst content in our sample using di erent indicators: the equivalent width of the polycyclic aromatic hydrocarbon at 6.2 m, the strength of the silicate feature at 9.7 m, and the steepness of the mid-IR spectra. We classified the spectra as SB-dominated and AGN-dominated, according to these diagnostics and compared the average mid-IR spectra of the various classes. Moreover, we studied the correlation between the 12 m luminosity, L (12 m), and the 2 10 keV energy band X-ray luminosity, LX(2 10 keV). Results. In 25 out of the 40 LINERs (i.e. 62.5%), the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is di erent from the average spectra of the other optical classes, showing a rather flat spectrum at 6 28 m. We find that the average spectrum of AGN-dominated LINERs with X-ray luminosities LX(2 10 keV) > 10 41 erg/s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. LX(2 10 keV) < 10 41 erg/s) show flat spectra di erent from any of the other optical classes. The correlation between L (12 m) and LX(2 10 keV) for AGN nicely extends towards low luminosities only if SB-dominated LINERs are excluded and if the 2 10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. Conclusions. We find that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence that the dusty-torus disappear when their bolometric luminosity is below Lbol ’ 10 42 erg/s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. To reconcile the Compton-thick nature of a large number of LINERs without dusty-torus signatures, we suggest that the material producing the Compton-thick X-ray obscuration is free of dust.Context. Most of the optically classified low ionisation narrow emission-line regions (LINERs) nuclei host an active galactic nuclei (AGN). However, how they fit into the unified model (UM) of AGN is still an open question. Aims. The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e hydrogen column densities of NH > 1:5 10 24 cm 2 ); and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. Methods. We have compiled all the available low spectral resolution mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PG QSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and Starburst (SBs) nuclei. We have studied the AGN versus the starburst content in our sample using di erent indicators: the equivalent width (EW) of the polycyclic aromatic hydrocarbon (PAH) at 6:2 m, the strength of the silicate feature at 9.7 m, and the steepness of the mid-IR spectra. We have classified the spectra as SB-dominated and AGNdominated, according to these diagnostics. We have compared the average mid-IR spectra of the various classes. Moreover, we have studied the correlation between the 12 m luminosity, L (12 m), and the 2-10 keV energy band X-ray luminosity, LX(2 10 keV). Results. In 25 out of the 40 LINERs (i.e., 62.5%) the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is di erent from the average spectra of the other optical classes, showing a rather flat spectrum at 6 28 m. We have found that the average spectrum of AGN-dominated LINERs with X-ray luminosities LX(2 10 keV) > 10 41 erg=s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. LX(2 10 keV) < 10 41 erg=s) show flat spectra di erent from any of the other optical classes. The correlation between L (12 m) and LX(2 10 keV) for AGN nicely extends toward low luminosities only if SB-dominated LINERs are excluded and the 2-10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. Conclusions. We have found that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence in favour of the dusty-torus disappearance when their bolometric luminosity is below Lbol’ 10 42 erg=s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. In order to reconcile the Compton-thick nature of a large fraction of LINERs with the lack of dusty-torus signatures, we suggest that the material producing the Compton-thick X-ray obscuration is free of dust.

Resolving the nuclear dust distribution of the Seyfert 2 galaxy NGC 3081

CRA acknowledges financial support from STFC (ST/G001758/1) and from the Spanish Ministry of Science and Innovation (MICINN) through project Consolider-Ingenio 2010 Programme grant CSD2006-00070: First Science with the GTC. AMPG and JIGS acknowledge the Spanish Ministry of Science and Innovation (MICINN) through project AYA2008-06311-C02-01/02. AAR acknowledges the Spanish Ministry of Science and Innovation through projects AYA2010-18029 (Solar Magnetism and Astrophysical Spectropolarimetry). AAH and PE acknowledges support from the Spanish Plan Nacional de Astronomia y Astrofisica under grant AYA2009-05705-E. MP acknowledges Junta de Andalucia and Spanish Ministry of Science and Innovation through projects PO8-TIC-03531 and AYA2010-15169. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy) and CICYT/MCYT (Spain). SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including University of Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, University of Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, University of Sussex (UK); and Caltech, JPL, NHSC, University of Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy);MCINN (Spain); SNSB (Sweden); STFC (UK) andNASA(USA).

INFRARED AND OPTICAL POLARIMETRY AROUND THE LOW-MASS STAR-FORMING REGION NGC 1333 IRAS 4A

We performed J- and R-band linear polarimetry with the 4.2 m William Herschel Telescope at the Observatorio del Roque de los Muchachos and with the 1.6 m telescope at the Observatorio do Pico dos Dias, respectively, to derive the magnetic field geometry of the diffuse molecular cloud surrounding the embedded protostellar system NGC 1333 IRAS 4A. We obtained interstellar polarization data for about three dozen stars. The distribution of polarization position angles has low dispersion and suggests the existence of an ordered magnetic field component at physical scales larger than the protostar. Some of the observed stars present intrinsic polarization and evidence of being young stellar objects. The estimated mean orientation of the interstellar magnetic field as derived from these data is almost perpendicular to the main direction of the magnetic field associated with the dense molecular envelope around IRAS 4A. Since the distribution of the CO emission in NGC 1333 indicates that the diffuse molecular gas has a multi-layered structure, we suggest that the observed polarization position angles are caused by the superposed projection of different magnetic field components along the line of sight.