The Herschel Orion Protostar Survey (HOPS, KPOT_tmegeath_2) is a sample of 410 young stellar objects (YSOs) in the Orion molecular clouds, selected from Spitzer data. Most objects have near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX; thus, the SEDs cover 1.2 - 870 microns and are used to classify the sample into protostellar classes. Of the 410 YSOs, 330 have Spitzer and Herschel data and are mostly protostars; the remaining objects include likely extragalactic contaminants and faint YSOs. Using mid-IR spectral indices and bolometric temperatures, the sample of 330 YSOs is classified into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II re-main-sequence stars. HOPS also implements a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30,400 model SEDs and uses it to determine the best-fit model parameters for each protostar.
This table contains the 2MASS, Spitzer, Herschel, and APEX source fluxes, as well as the rebinned IRS fluxes, of the 410 HOPS sources. Note that not every source has data at all of these wavelengths.
The Herschel Orion Protostar Survey (HOPS, KPOT_tmegeath_2) is a sample of 410 young stellar objects (YSOs) in the Orion molecular clouds, selected from Spitzer data. Most objects have near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX; thus, the SEDs cover 1.2 - 870 microns and are used to classify the sample into protostellar classes. Of the 410 YSOs, 330 have Spitzer and Herschel data and are mostly protostars; the remaining objects include likely extragalactic contaminants and faint YSOs. Using mid-IR spectral indices and bolometric temperatures, the sample of 330 YSOs is classified into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II re-main-sequence stars. HOPS also implements a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30,400 model SEDs and uses it to determine the best-fit model parameters for each protostar.
This table contains the SED class, bolometric luminosity and temperature, mid-IR spectral index, and best-fit model parameters for the 330 YSOs with Spitzer and Herschel data.
We present coordinates and brightness estimates for 4175 candidate field horizontal-branch and A-type stars, in the magnitude range 10<=B<=15.5, selected using an objective-prism/interference-filter survey technique. The candidates lie primarily in the northern Galactic hemisphere and complement a previously published sample of southern Galactic hemisphere candidates. Available spectroscopy and photometry indicates that the great majority of the candidates are likely to be bona fide members of either the field blue horizontal- branch population or the blue, metal-deficient, high surface gravity stars referred to by Preston, Beers, & Schectman (1994AJ....108..538P) as BMP stars. The remaining stars in the catalog are likely to be a mix of metal-deficient turnoff stars, metallic-line (Am) stars, field red horizontal-branch stars, optical doubles with overlapping objective-prism spectra, and (particularly among the fainter candidates) inadvertently included late-type stars.
We obtained high-resolution spectra for 94 candidate stars belonging to the HB of M 22 with FLAMES. Previous works have indicated that this cluster has split subgiant (SGB) and red giant branches (RGB) and hosts two different stellar populations, differing in overall metal abundance and both exhibiting a Na-O anti-correlation. The HB stars we observed span a restricted temperature range (7800<Teff<11000K), where about 60% of the HB stars of M 22 are. Within our sample, we can distinguish three groups of stars segregated (though contiguous) in colours: Group 1 (49 stars) is metal-poor, N-normal, Na-poor and O-rich: our abundances for this (cooler) group match very well those determined for the primordial group of RGB stars (a third of the total) from previous studies. Group 2 (23 stars) is still metal-poor, but it is N- and Na-rich, though only very mildly depleted in O. We can identify this intermediate group as the progeny of the metal-poor RGB stars that occupy an intermediate location along the Na-O anti-correlation and include about 10% of the RGB stars. The third group (20 stars) is metal-rich, Na-rich, and O-rich. This hotter group likely corresponds to the most O-rich component of the previously found metal-rich RGB population (a quarter of the total). We did not observe any severely O-depleted stars and we think that the progeny of these stars falls on the hotter part of the HB. Furthermore, we found that the metal-rich population is also over-abundant in Sr, in agreement with results for corresponding RGB and SGB stars. However, we do not find any significant variation in the ratio between the sum of N and O abundances to Fe. We do not have C abundances for our stars. There is some evidence of an enhancement of He content for Groups 2 and 3 stars (Y=0.338+/-0.014+/-0.05); the error bar due to systematics is large, but a consistent analysis of data for several GCs confirms that stars in these groups within M22 are likely overabundant in He. We conclude that on the whole, our results agree with the proposition that chemical composition drives the location of stars along the HB of a GC. Furthermore, we found a number of fast rotators. They are concentrated in a restricted temperature range along the HB of M22. Fast rotating stars might be slightly less massive and bluer than slowly rotating ones, but other interpretations are possible.
The chemical composition of horizontal branch (HB) stars might help to clarify the formation history of individual globular clusters (GCs). We studied the Na-O anti-correlation from moderately high resolution spectra for 91 stars on the bimodal HB of NGC 1851; in addition we observed 13 stars on the lower red giant branch (RGB). In our HB sample, 35 stars are on the blue HB (BHB), one is an RR Lyrae, and 55 stars are on the red HB (RHB). The ratio of BHB to RHB stars is close to the total in the cluster (35 and 54%, respectively), while RR Lyrae variables are under-represented, (they are ~12% of the NGC 1851 stars). We also derived abundances for He and N in BHB stars.
We used FLAMES+GIRAFFE (Medusa mode) at the VLT to obtain moderately high resolution spectra for 30 red horizontal branch (RHB) stars, 4 RR Lyrae variables, and 17 blue horizontal branch (BHB) stars in the low-concentration, moderately metal-rich globular cluster NGC 6723 ([Fe/H]=-1.22+/-0.08 from our present sample). The spectra were optimized to derive O and Na abundances. In addition, we obtained abundances for other elements, including N, Fe, Mg, Ca, Ni, and Ba. We used these data to discuss the evidence of a connection between the distribution of stars along the horizontal branch (HB) and the multiple populations that are typically present in globular clusters. We found that all RHB and most (13 out of 17) BHB stars are O-rich, Na-poor, and N-poor; these stars probably belong to the first stellar generation in this cluster. Only the four warmest observed stars are (moderately) O-poor, Na-rich, and N-rich, and they probably belong to the second generation. While our sample is not fully representative of the whole HB population in NGC 6723, our data suggest that in this cluster only HB stars warmer than ~9000K, that is one fourth of the total, belong to the second generation, if at all. Since in many other clusters this fraction is about two thirds, we conclude that the fraction of first/second generation in globular clusters may be strongly variable. In addition, the wide range in colour of chemically homogeneous first-generation HB stars requires a considerable spread in mass loss (>0.10M_{sun}_). The reason for this spread is yet to be understood. Finally, we found a high Ba abundance, with a statistically significant radial abundance gradient.
Globular clusters have been recognized to host multiple stellar populations. A spectacular example of this is the massive cluster NGC 2808, where multiple populations have been found along the horizontal branch (HB) and the main sequence (MS). Studies of red giants showed that this cluster appears homogeneous insofar Fe abundance is concerned, but it shows an extended anticorrelation between Na and O abundances. The Na-poor, O-rich population can be identified with the red MS, and the Na-rich, O-poor one with the blue one. This may be understood in terms of different He content, He being correlated with Na. A prediction of this scenario is that He-rich, Na-rich He-core burning stars, because they are less massive, will end up on the bluer part of the HB, while He-poor, Na-poor stars will reside on the red HB. The aim of this paper is to verify this prediction. To this purpose, we acquired high-resolution spectra of regions including strong O and Na lines in several tens of HB stars of NGC 2808, sampling both the red and blue parts of the HB.
To check the impact of the multiple population scenario for globular clusters on their horizontal branch (HB), we present an analysis of the composition of 110 red HB (RHB) stars in 47 Tucanae and of 61 blue HB (BHB) and 30 RHB stars in M5. In 47 Tuc we found tight relations between the colours of the stars and their abundances of p-capture elements. This strongly supports the idea that the He content - which is expected to be closely correlated with the abundances of p-capture elements - is the third parameter (after overall metallicity and age) that determines the colour of HB stars. However, the range in He abundance must be small ({Delta}Y<0.03) in 47 Tuc to reproduce our observations; this agrees with previous analyses. There is possibly a correlation between the abundances of p- and n-capture elements in 47 Tuc. If confirmed, this might suggest that asymptotic giant branch stars of moderate mass contributed to the gas from which second-generation stars formed. Considering the selection effects in our sample (which does not include stars warmer than 11000K and RR Lyrae variables, which were excluded because we could not obtain accurate abundances with the adopted observing procedure) is important to understand our results for M5. In this case, we find that, as expected, RHB stars are Na-poor and O-rich, and likely belong to the primordial population. There is a clear correlation of the [Na/O] ratio and N abundance with colour along the BHB. A derivation of the He abundance for these stars yields a low value of Y=0.22+/-0.03. This is expected because HB stars of a putative He-rich population in this cluster should be warmer than 11000K, and would accordingly not have been sampled by our analysis. However, we need some additional source of scatter in the total mass loss of stars climbing up the red giant branch to reproduce our results for M5. Finally, we found a C-star on the HB of 47Tuc and a Ba-rich, fast-rotating, likely binary star on the HB of M5. These stars are among the brightest and coolest HB stars.
Theoretical models and laboratory experiments show that CH_3_OH is efficiently formed on cold grain surfaces through the successive hydrogenation of CO, forming HCO and H_2_CO as intermediate species. In cold cores and low UV-field illumination photo-dissociation regions (PDRs) the ices can be released into the gas-phase through nonthermal processes such as photodesorption, which considerably increases their gas-phase abundances. We investigate the dominant formation mechanism of H_2_CO and CH_3_OH in the Horsehead PDR and its associated dense core.
We present first results of the H_2_O Southern Galactic Plane Survey (HOPS), using the Mopra Radio Telescope with a broad-band backend and a beam size of about 2arcmin. We have observed 100deg^2^ of the southern Galactic plane at 12mm (19.5-27.5GHz), including spectral line emission from H_2_O masers, multiple metastable transitions of ammonia, cyanoacetylene, methanol and radio recombination lines. In this paper, we report on the characteristics of the survey and H2O maser emission. We find 540 H_2_O masers, of which 334 are new detections.