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Alberto Noriega-Crespo

Publications and source records attributed to Alberto Noriega-Crespo.

53 records · Page 3Linked to original sources

The Spitzer survey of interstellar clouds in the Gould Belt. II. The Cepheus Flare observed with IRAC and MIPS

We present Spitzer IRAC (~2 deg^2) and MIPS (~8 deg^2) observations of the Cepheus Flare which is associated with the Gould Belt, at an approximate distance of ~300 pc. Around 6500 sources are detected in all four IRAC bands, of which ~900 have MIPS 24 micron detections. We identify 133 YSO candidates using color-magnitude diagram techniques, a large number of the YSO candidates are associated with the NGC 7023 reflection nebula. Cross identifications were made with the Guide Star Catalog II and the IRAS Faint Source Catalog, and spectral energy distributions (SED) were constructed. SED modeling was conducted to estimate the degree of infrared excess. It was found that a large majority of disks were optically thick accreting disks, suggesting that there has been little disk evolution in these sources. Nearest-neighbor clustering analysis identified four small protostellar groups (L1228, L1228N, L1251A, and L1251B) with 5-15 members each and the larger NGC 7023 association with 32 YSO members. The star formation efficiency for cores with clusters of protostars and for those without clusters was found to be ~8% and ~1% respectively. The cores L1155, L1241, and L1247 are confirmed to be starless down to our luminosity limit of L_bol=0.06 L_sol.

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Far-infrared Observations of the Very Low-Luminosity Embedded Source L1521F-IRS in the Taurus Star-Forming Region

We investigate the environment of the very low-luminosity object L1521F IRS using data from the Taurus Spitzer Legacy Survey. The MIPS 160 micron image shows both extended emission from the Taurus cloud as well as emission from multiple cold cores over a 1 X 2 deg region. Analysis shows that the cloud dust temperature is 14.2 +- 0.4 K and the extinction ratio is A_160/A_K = 0.010 +- 0.001 up to A_V ~ 4 mag. We find kappa_160 = 0.23 +- 0.046 cm^2/g for the specific opacity of the gas-dust mixture. Therefore, for dust in the Taurus cloud we find the 160 um opacity is significantly higher than that measured for the diffuse ISM, but not too different from dense cores, even at modest extinction values. Furthermore, the 160 um image shows features that do not appear in the IRAS 100 um image. We identify six regions as cold cores, i.e. colder than 14.2 K, all of which have counterparts in extinction maps or C18O maps. We compare the effects of L1521F IRS on its natal core and find there is no evidence for dust heating at 160 or 100 um by the embedded source. From the infrared luminosity L_TIR = 0.024 Lo we find L_bol = 0.034 - 0.046L_o, thus confirming the source's low-luminosity. Comparison of L1521F IRS with theoretical simulations for the very early phases of star formation appears to rule out the first core collapse phase. The evolutionary state appears similar to or younger than the class 0 phase, and the estimated mass is likely to be substellar.

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A Direct Measurement of the Dust Extinction Curve in an Intermediate-Redshift Galaxy

We present a proof-of-concept study that dust extinction curves can be extracted from the infrared (IR), optical, ultraviolet (UV) and X-ray afterglow observations of GRBs without assuming known extinction laws. We focus on GRB 050525A (z = 0.606), for which we also present IR observations from the Spitzer Space Telescope at about 2.3 days post-burst. We construct the spectral energy distribution (SED) of the afterglow and use it to derive the dust extinction curve of the host galaxy in 7 optical/UV wavebands. By comparing our derived extinction curve to known templates, we see that the Galactic or Milky Way extinction laws are disfavored versus the Small and Large Magellanic Cloud (SMC and LMC) ones, but that we cannot rule out the presence of a LMC-like 2175 angstrom bump in our extinction curve. The dust-to-gas ratio present within the host galaxy of GRB 050525A is similar to that found in the LMC, while about 10 to 40% more dust is required if the SMC template is assumed. Our method is useful to observatories that are capable of simultaneously observing GRB afterglows in multiple wavebands from the IR to the X-ray.

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The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VII. Ophiuchus Observed with MIPS

We present maps of 14.4 deg^2 of the Ophiuchus dark clouds observed by the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). These high quality maps depict both numerous point sources as well as extended dust emission within the star-forming and non-star-forming portions of these clouds. Using PSF-fitting photometry, we detect 5779 sources at 24 um and 81 sources at 70 um at the 10 sigma level of significance. Three hundred twenty-three candidate young stellar objects (YSOs) were identified according to their positions on the MIPS/2MASS K versus K$-$[24] color-magnitude diagrams as compared to 24 um detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all the ones with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates.

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The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. IV. Lupus Observed with MIPS

We present maps of 7.78 square degrees of the Lupus molecular cloud complex at 24, 70, and $160\:μ$m. They were made with the Spitzer Space Telescope's Multiband Imaging Photometer for Spitzer (MIPS) instrument as part of the Spitzer Legacy Program, ``From Molecular Cores to Planet-Forming Disks'' (c2d). The maps cover three separate regions in Lupus, denoted I, III, and IV. We discuss the c2d pipeline and how our data processing differs from it. We compare source counts in the three regions with two other data sets and predicted star counts from the Wainscoat model. This comparison shows the contribution from background galaxies in Lupus I. We also create two color magnitude diagrams using the 2MASS and MIPS data. From these results, we can identify background galaxies and distinguish them from probable young stellar objects. The sources in our catalogs are classified based on their spectral energy distribution (SED) from 2MASS and Spitzer wavelengths to create a sample of young stellar object candidates. From 2MASS data, we create extinction maps for each region and note a strong corresponence between the extinction and the $160\:μ$m emission. The masses we derived in each Lupus cloud from our extinction maps are compared to masses estimated from $^{13}$CO and C$^{18}$O and found to be similar to our extinction masses in some regions, but significantly different in others. Finally, based on our color-magnitude diagrams, we selected 12 of our reddest candidate young stellar objects for individual discussion. Five of the 12 appear to be newly-discovered YSOs.

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Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 micron Imaging

The absolute calibration and characterization of the Multiband Imaging Photometer for Spitzer (MIPS) 70 micron coarse- and fine-scale imaging modes are presented based on over 2.5 years of observations. Accurate photometry (especially for faint sources) requires two simple processing steps beyond the standard data reduction to remove long-term detector transients. Point spread function (PSF) fitting photometry is found to give more accurate flux densities than aperture photometry. Based on the PSF fitting photometry, the calibration factor shows no strong trend with flux density, background, spectral type, exposure time, or time since anneals. The coarse-scale calibration sample includes observations of stars with flux densities from 22 mJy to 17 Jy, on backgrounds from 4 to 26 MJy sr^-1, and with spectral types from B to M. The coarse-scale calibration is 702 +/- 35 MJy sr^-1 MIPS70^-1 (5% uncertainty) and is based on measurements of 66 stars. The instrumental units of the MIPS 70 micron coarse- and fine-scale imaging modes are called MIPS70 and MIPS70F, respectively. The photometric repeatability is calculated to be 4.5% from two stars measured during every MIPS campaign and includes variations on all time scales probed. The preliminary fine-scale calibration factor is 2894 +/- 294 MJy sr^-1 MIPS70F^-1 (10% uncertainty) based on 10 stars. The uncertainty in the coarse- and fine-scale calibration factors are dominated by the 4.5% photometric repeatability and the small sample size, respectively. The 5-sigma, 500 s sensitivity of the coarse-scale observations is 6-8 mJy. This work shows that the MIPS 70 micron array produces accurate, well calibrated photometry and validates the MIPS 70 micron operating strategy, especially the use of frequent stimulator flashes to track the changing responsivities of the Ge:Ga detectors.

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Tentative Discovery of a New Supernova Remnant in Cepheus: Unveiling an Elusive Shell in the Spitzer Galactic First Look Survey

We have discovered an axially symmetric, well-defined shell of material in the constellation of Cepheus, based on imaging acquired as part of the Galactic First Look Survey with the Spitzer Space Telescope. The 86'' x 75'' object exhibits brightened limbs on the minor axis, and is clearly visible at 24 microns, but is not detected in the 3.6, 4.5, 5.8, 8.0, 70, or 160 micron images. Followup with 7.5 - 40 micron spectroscopy reveals the shell to be composed entirely of ionized gas, and that the 24 micron imaging traces solely [O IV] 25.89 micron emission. The spectrum also exhibits weaker [Ne III], [S III], and very weak [Ne V] emission. No emission from warm dust is detected. Spectral cuts through the center of the shell and at the northern limb are highly consistent with each other. The progenitor is not readily identified, but with scaling arguments and comparison to well-known examples of evolved stellar objects, we find the observations to be most straightforward to interpret in terms of a young supernova remnant located at a distance of at least 10 kpc, some 400 pc above the Galactic disk. If confirmed, this would be the first SNR discovered initially at infrared wavelengths.

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Protostars in the Elephant Trunk Nebula

The optically-dark globule IC 1396A is revealed using Spitzer images at 3.6, 4.5, 5.8, 8, and 24 microns to be infrared-bright and to contain a set of previously unknown protostars. The mid-infrared colors of the 24 microns detected sources indicate several very young (Class I or 0) protostars and a dozen Class II stars. Three of the new sources (IC 1396A: gamma, delta, and epsilon) emit over 90% of their bolometric luminosities at wavelengths greater than 3 microns, and they are located within ~0.02 pc of the ionization front at the edge of the globule. Many of the sources have spectra that are still rising at 24 microns. The two previously-known young stars LkHa 349 a and c are both detected, with component c harboring a massive disk and component a being bare. Of order 5% of the mass of material in the globule is presently in the form of protostars in the 10^5 to 10^6 yr age range. This high star formation rate was likely triggered by radiation from a nearby O star.

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A mid-IR survey of the L 1641-N region with ISOCAM

We present an analysis of the L 1641 outflow region using broad-band and narrow-band imaging data at mid-infrared wavelengths from ISOCAM. We detect a total of 34 sources in the $7.65^{\prime}$ x $8.40^{\prime}$ region covered by the broad-band filters. Four of these sources have no reported detection in previous studies of the region. We find that the source previously identified as the near-IR counter-part to the IRAS detected point-source (IRAS 05338-0624) is not the brightest source in the wavelength region of the IRAS 12 \micron\ filter. We find instead that a nearby object (within the beam of IRAS and not detected at near-IR wavelengths) outshines all others sources in the area by a factor of $\sim$2. We submit that this source is likely to be the IRAS detected point source. A comparison of the near-IR (J-H vs H-K) and mid-IR (J-K vs [6.7 um]-[14 um]) color-color plots shows only four sources with excess emission at near-IR wavelengths, but atleast 85% of all sources show excess emission at mid-IR wavelengths. The CVF spectra suggest a range of evolutionary status in the program stars ranging from embedded YSOs to the young disks. When combined with optical and near-IR age estimates, these results show active current star-formation in the region that has been on-going for at least 2 Myr.

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New debris disk candidates: 24 micron stellar excesses at 100 Myr

Sixty three members of the 100 Myr old open cluster M47 (NGC 2422) have been detected at 24 micron with Spitzer. The Be star V 378 Pup shows an excess both in the near-infrared and at 24 micron (K-[24] = 2.4 mag), probably due to free-free emission from the gaseous envelope. Seven other early-type stars show smaller excesses, K-[24] = 0.6-0.9. Among late-type stars, two show large excesses: P922 - a K1V star with K-[24] = 1.08 pm 0.11 and P1121 - an F9V star with K-[24] = 3.72 pm 0.02. P1121 is the first known main-sequence star showing an excess comparable to that of beta Pic, which may indicate the presence of an exceptionally massive debris disk. It is possible that a major planetesimal collision has occurred in this system, consistent with the few hundred Myr time scales estimated for the clearing of the Solar System.

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Confirmation of SBS 1150+599A As An Extremely Metal-Poor Planetary Nebula

SBS 1150+599A is a blue stellar object at high galactic latitude discovered in the Second Byurakan Survey. New high-resolution images of SBS 1150+599A are presented, demonstrating that it is very likely to be an old planetary nebula in the galactic halo, as suggested by Tovmassian et al (2001). An H-alpha image taken with the WIYN 3.5-m telescope and its "tip/tilt" module reveals the diameter of the nebula to be 9.2", comparable to that estimated from spectra by Tovmassian et al. Lower limits to the central star temperature were derived using the Zanstra hydrogen and helium methods to determine that the star's effective temperature must be > 68,000K and that the nebula is optically thin. New spectra from the MMT and FLWO telescopes are presented, revealing the presence of strong [Ne V] lambda 3425, indicating that the central star temperature must be > 100,000K. With the revised diameter, new central star temperature, and an improved central star luminosity, we can constrain photoionization models for the nebula significantly better than before. Because the emission-line data set is sparse, the models are still not conclusive. Nevertheless, we confirm that this nebula is an extremely metal-poor planetary nebula, having a value for O/H that is less than 1/100 solar, and possibly as low as 1/500 solar.

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Far Infrared Spectroscopy of the HH 1/2 Outflow

The HH 1/2 system has been observed with the two spectrometers on board the Infrared Space Observatory. Diffuse [CII] 158um emission indicate the presence of a Photo-Dissociation Region (PDR) which is only in part due to the external Far-UV irradiation from the nearby Orion Nebula. Additional irradiation must be originated locally and we show that the FUV field produced in the recombination regions behind the shocks traced by the HH objects is sufficient to induce a PDR at the flow cavity walls. The analysis of [OI], [SiII]34.8um and [NeII] 12.8um lines suggests shock velocities v=100-140 km/s with pre-shock densities between 100 and 1000 per cc. H2 pure rotational lines trace a T=600 K gas which is likely to be warmed up in slow, planar, molecular shocks. The coexistence in the areas subtended by the instrumental beamsizes of shocks at different velocities is consistent with the bow-shock morphology of the HH 1 and, to a lesser extent, HH 2 as traced by optical images.

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The Optical Proper Motions of HH 7-11 and Cep E (HH 377)

A key ingredient in understanding the dynamics of stellar outflows is their proper motion. We have used optical images in the [SII] emission at 6717/31 A and the red Digitized Palomar Observatory Sky Survey (DSS) plates to determine the proper motion of HH 7-11 system and the optical knot of Cep E (HH 377). The DSS plate measurements span nearly 37 years for both HH 7-11 and HH 377 and have wide field of view, which allows an accurate determination of the proper motions despite their relatively low angular resolution. The optical images, with higher angular resolution, cover a shorter period of 7 and 4 years, respectively, and have been used to complement the DSS measurements. From the DSS plates we have found that HH 377 has a proper motion of 0.031 +/- 0.003 arcsec/yr with a PA = 206 arcdeg, i.e. moving away from IRAS 230111+63, that at a distance of 730 pc corresponds to a tangential velocity of 107 +/- 14 km/s. The values obtained from the optical images are consistent with these measurements. Similarly, the proper motions of HH 7-11 range from 0.015 +/- 0.009 (HH 9) to 0.044 +/- 0.007 (HH 11) arcsec/yr, and the flow is moving away from SVS 13 with a mean PA = 136 arcdeg. At a distance of 330 pc, these motions correspond to tangential velocities of 25 - 70 km/s, i.e. comparable to the original values obtained by Herbig & Jones (1983). The measurements from the optical CCD [SII] images are again consistent with these motions, although in detail there are some difference, particularly for HH 7 and HH 10.

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Spectroscopy of Stellar Jets, Outflows, and Young Stellar Objects with the Infrared Space Observatory

The Infrared Space Observatory (ISO) was an extremely successful european space mission that gave us an unparallel view of the Universe in the infrared, and provided us with hundreds of observations of star forming regions and bipolar outflows. Three of the instrument teams, in charge of the infrared camera (CAM) and the two spectrometers at short and long wavelengths (SWS and LWS respectively), used a significant fraction of their guarantee time to study YSOs and outflows spectroscopically. In here, I will briefly review some of their main findings, particularly the detection of water, H2 rotational emission lines and the presence of other complex molecules. I will present new spectroscopic results on HH 1-2, HH 7-11 and Cep E, and their sources. And finally, I will discuss some of the general trends derived from these observations and their relevance in understanding the emission from these objects using J and C shock models.

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A Shock-Induced PDR in the HH 80/81 Flow. Far Infrared Spectroscopy

The two spectrometers on board the Infrared Space Observatory were used to observe the Herbig-Haro objects HH 80, 81 and 80N, as well as their candidate exciting source IRAS 18162-2048. The fine structure lines of [OI]63um, [OI]145um and [CII]158um are detected everywhere, while [NII]122um and [OIII]88um are only detected toward the HH objects; line ratios confirm for the first time the collisionally excited HH nature of HH 80N. No molecular line is detected in any of the observed positions. We use a full shock code to diagnose shock velocities vs~100 km/s toward the HH objects, as expected from the optical spectroscopy. Since proper motions suggest velocities in excess of 600 km/s, the HH objects probably represent the interface between two flow components with velocity differing by ~vs. Aside from the flow exciting source, the [CII]158um line is everywhere brighter than the [OI]63um line, indicating the presence of a Photo-Dissociation Region (PDR) all along the flow. Continuum emission from the HH objects and from other positions along the flow is only detected longword of ~50 micron, and its proportionality to the [CII]158um line flux suggests it is PDR in origin. We propose that the FUV continuum irradiated by the HH objects and the jet is responsible for the generation of a PDR at the walls of the flow cavity. We develop a very simple model which strengthens the plausibility of this hypothesis.

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ISOCAM Molecular Hydrogen Images of the Cep E Outflow

The physical characteristics of Cepheus E (Cep E) `embedded' outflow are analyzed using ISOCAM images in the v=0-0 S(5) 6.91 um and S(3) 9.66 um molecular hydrogen lines. We find that the morphology of the Cep E outflow in the ground vibrational H2 lines is similar to that of the near infrared v=1-0 2.12 um line. At these mid-IR wavelengths, we do not detect the second H2 outflow which is almost perpendicular to Cep E 2.121 um flow or traces of H2 emission along the second 12CO J = 2-1 outflow at 52 degrees angle, down to a surface brightness of 12 - 46 uJy/arcsec square. We do detect at 6.91 um the likely source of the main H2 and CO outflows, IRAS 23011+6126, and show that the source is easily seen in all IRAS bands using HiRes images. The source is not detected at 9.66 um, but we think this agrees with the interstellar extinction curve which has a minimum at 7 um, but rises a 9.7 um due to the strong absorption silicate feature, enhanced in this case by a cocoon surrounding the Class 0 object. This idea is supported by our models of the spectral energy distribution (SED) of the central object. The models assume that the main source of opacity is due to bare silicates and our best fit for the SED yields a total mass of envelope of 17 solar masses and a dust temperature of 18 K.

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Photo-evaporation of clumps in Planetary Nebulae

We study the evolution of dense neutral clumps located in the outer parts of planetary nebulae. These clumps will be photo-ionized by the ionizing radiation from the central star and change their structure in the process. The main effect of the ionization process is the setting up of a photo-evaporation flow and a shock running through the clump. Once this shock has moved through the entire clump it starts to accelerate because of the `rocket effect'. This continues until the entire clump has been photo-ionized. We present an analytic model for the shock and accelerating phases and also the results of numerical simulations which include detailed microphysics. We find a good match between the analytic description and the numerical results and use the numerical results to produce some of the clump's observational characteristics at different phases of its evolution. We compare the results with the properties of the fast moving low ionization knots (ansae or FLIERs) seen in a number of planetary nebulae. We find that the models match many of the kinematic and emission properties of FLIERs.

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