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Register a new userPredicted Colors and Flux Densities of Protostars in the Herschel PACS and SPIRE Filters
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Upcoming surveys with the Herschel Space Observatory will yield far-IR photometry of large samples of young stellar objects, which will require careful interpretation. We investigate the color and luminosity diagnostics based on Herschel broad-band filters to identify and discern the properties of low-mass protostars. We compute a grid of 2,016 protostars in various physical congurations, present the expected flux densities and flux density ratios for this grid of protostars, and compare Herschel observations of three protostars to the model results. These provide useful constraints on the range of colors and fluxes of protostar in the Herschel filters. We find that Herschel data alone is likely a useful diagnostic of the envelope properties of young stars
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We present full spectral scans from 200-670$mu$m of 26 Class 0+I protostellar sources, obtained with $Herschel$-SPIRE, as part of the COPS-SPIRE Open Time program, complementary to the DIGIT and WISH Key programs. Based on our nearly continuous, line-free spectra from 200-670 $mu$m, the calculated bolometric luminosities ($L_{rm bol}$) increase by 50% on average, and the bolometric temperatures ($T_{rm bol}$) decrease by 10% on average, in comparison with the measurements without Herschel. Fifteen protostars have the same Class using $T_{rm bol}$ and $L_{rm bol}$/$L_{rm submm}$. We identify rotational transitions of CO lines from J=4-3 to J=13-12, along with emission lines of $^{13}$CO, HCO$^+$, H$_{2}$O, and [CI]. The ratios of $^{12}$CO to $^{13}$CO indicate that $^{12}$CO emission remains optically thick for $J_{rm up}$ < 13. We fit up to four components of temperature from the rotational diagram with flexible break points to separate the components. The distribution of rotational temperatures shows a primary population around 100 K with a secondary population at $sim$350 K. We quantify the correlations of each line pair found in our dataset, and find the strength of correlation of CO lines decreases as the difference between $J$-level between two CO lines increases. The multiple origins of CO emission previously revealed by velocity-resolved profiles are consistent with this smooth distribution if each physical component contributes to a wide range of CO lines with significant overlap in the CO ladder. We investigate the spatial extent of CO emission and find that the morphology is more centrally peaked and less bipolar at high-$J$ lines. We find the CO emission observed with SPIRE related to outflows, which consists two components, the entrained gas and shocked gas, as revealed by our rotational diagram analysis as well as the studies with velocity-resolved CO emission.
Herschel PACS and SPIRE images have been obtained over a 30x30 area around the well-known carbon star CW Leo (IRC +10 216). An extended structure is found in an incomplete arc of ~22 diameter, which is cospatial with the termination shock due to interaction with the interstellar medium (ISM) as defined by Sahai & Chronopoulos from ultraviolet GALEX images. Fluxes are derived in the 70, 160, 250, 350, and 550 um bands in the region where the interaction with the ISM takes place, and this can be fitted with a modified black body with a temperature of 25+-3 K. Using the published proper motion and radial velocity for the star, we derive a heliocentric space motion of 25.1 km/s. Using the PACS and SPIRE data and the analytical formula of the bow shock structure, we infer a de-projected standoff distance of the bow shock of R0 = (8.0+-0.3)x10^17 cm. We also derive a relative velocity of the star with respect to the ISM of (106.6+-8.7)/sqrt(n_ISM) km/s, where n_ISM is the number density of the local ISM.
In this paper we will discuss the images of Planetary Nebulae that have recently been obtained with PACS and SPIRE on board the Herschel satellite. This comprises results for NGC 650 (the little Dumbbell nebula), NGC 6853 (the Dumbbell nebula), and NGC 7293 (the Helix nebula).
Far-infrared spectroscopy reveals gas cooling and its underlying heating due to physical processes taking place in the surroundings of protostars. These processes are reflected in both the chemistry and excitation of abundant molecular species. Here, we present the Herschel-PACS far-IR spectroscopy of 90 embedded low-mass protostars from the WISH (van Dishoeck et al. 2011), DIGIT (Green et al. 2013), and WILL surveys (Mottram et al. 2017). The $5times5$ spectra covering the $sim50times50$ field-of-view include rotational transitions of CO, H$_2$O, and OH lines, as well as fine-structure [O I] and [C II] in the $sim$50-200 $mu$m range. The CO rotational temperatures (for $J_mathrm{u}geq14)$ are typically $sim$300 K, with some sources showing additional components with temperatures as high as $sim$1000 K. The H$_2$O / CO and H$_2$O / OH flux ratios are low compared to stationary shock models, suggesting that UV photons may dissociate some H$_2$O and decrease its abundance. Comparison to C shock models illuminated by UV photons shows good agreement between the line emission and the models for pre-shock densities of $10^5$ cm$^{-3}$ and UV fields 0.1-10 times the interstellar value. The far-infrared molecular and atomic lines are the unique diagnostic of shocks and UV fields in deeply-embedded sources.
The density and temperature structures of dense cores in the L1495 cloud of the Taurus star-forming region are investigated using Herschel SPIRE and PACS images in the 70 $mu$m, 160 $mu$m, 250 $mu$m, 350 $mu$m and 500 $mu$m continuum bands. A sample consisting of 20 cores, selected using spectral and spatial criteria, is analysed using a new maximum likelihood technique, COREFIT, which takes full account of the instrumental point spread functions. We obtain central dust temperatures, $T_0$, in the range 6-12 K and find that, in the majority of cases, the radial density falloff at large radial distances is consistent with the $r^{-2}$ variation expected for Bonnor-Ebert spheres. Two of our cores exhibit a significantly steeper falloff, however, and since both appear to be gravitationally unstable, such behaviour may have implications for collapse models. We find a strong negative correlation between $T_0$ and peak column density, as expected if the dust is heated predominantly by the interstellar radiation field. At the temperatures we estimate for the core centres, carbon-bearing molecules freeze out as ice mantles on dust grains, and this behaviour is supported here by the lack of correspondence between our estimated core locations and the previously-published positions of H$^{13}$CO$^+$ peaks. On this basis, our observations suggest a sublimation-zone radius typically $sim 10^4$ AU. Comparison with previously-published N$_2$H$^+$ data at 8400 AU resolution, however, shows no evidence for N$_2$H$^+$ depletion at that resolution.
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