- ID:
- ivo://CDS.VizieR/J/MNRAS/448/464
- Title:
- JHK lightcurves of red giants in the SMC
- Short Name:
- J/MNRAS/448/464
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Long-term JHK light curves have recently become available for large numbers of the more luminous stars in the Small Magellanic Cloud (SMC). We have used these JHK light curves, along with OGLE (Optical Gravitational Lensing Experiment) V and I light curves, to examine the variability of a sample of luminous red giants in the SMC which show prominent long secondary periods (LSPs). The origin of the LSPs is currently unknown. In oxygen-rich stars, we found that while most broad-band colours (e.g. V- I) get redder when an oxygen-rich star dims during its LSP cycle, the J-K colour barely changes and sometimes becomes bluer. We interpret the J-K colour changes as being due to increasing water vapour absorption during declining light caused by the development of a layer of dense cool gas above the photosphere. This result and previous observations which indicate the development of a chromosphere between minimum to maximum light suggest that the LSP phenomenon is associated with the ejection of matter from the stellar photosphere near the beginning of light decline. We explore the possibility that broad-band light variations from the optical to the near-infrared regions can be explained by either dust absorption by ejected matter or large spots on a rotating stellar surface. However, neither model is capable of explaining the observed light variations in a variety of colour-magnitude diagrams. We conclude that some other mechanism is responsible for the light variations associated with LSPs in red giants.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/125/1940
- Title:
- JHKs photometry in LMC HII region N11B
- Short Name:
- J/AJ/125/1940
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The second largest H II region in the Large Magellanic Cloud, N11B (LHA 120-N 11B) has been surveyed in the near-IR. We present JHKs images of the N11B nebula. These images are combined with CO (1->0) emission-line data and with archival New Technology Telescope and Hubble Space Telescope WFPC2 optical images to address the star formation activity of the region. IR photometry of all the IR sources detected is given. We confirm that a second generation of stars is currently forming in the N11B region. Our IR images show the presence of several bright IR sources that appear to be located toward the molecular cloud as seen from the CO emission in the area.
- ID:
- ivo://CDS.VizieR/J/A+A/422/129
- Title:
- JHKs photometry in N159 (LMC)
- Short Name:
- J/A+A/422/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the Large Magellanic Cloud Papillon Nebula (N 159-5), a conspicuous High Excitation Blob (HEB) lying in the star forming complex N 159. Using JHK near-infrared photometry obtained at the ESO VLT with the ISAAC camera, we examine the stellar populations associated with the Papillon, tracing their history using stellar evolution models. Two populations are revealed: one composed of young, massive stars with an age ~3Myr, and a second consisting of older lower mass stars of age spreading between 1 and 10Gyr. We analyze the properties of those populations and discuss their significance in the context of N 159. We also estimate that if the star at the center of the Papillon is single its initial mass is ~50 solar masses and it is affected by an extinction Av~7mag.
- ID:
- ivo://CDS.VizieR/J/AJ/128/2239
- Title:
- JHKs photometry of 92 LMC Cepheids
- Short Name:
- J/AJ/128/2239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared J, H, and K_s_ photometric measurements of 92 Cepheids in the Large Magellanic Cloud are presented. The stars are spread over the face of the Cloud, their periods range from 3 to 100 days, and their light curves are sampled at an average of 22 phase points per star. The intensity-weighted mean magnitudes and colors define period-luminosity-color (PL or PLC) relations whose uncertainties due to differential metal abundance and reddening/extinction effects are minimal. The dispersions in the infrared PL, PLC, and extinction-free period-Wesenheit relations are extremely small, amounting to less than 0.10mag (or 5% in distance).
- ID:
- ivo://CDS.VizieR/J/A+A/462/599
- Title:
- JHKs photometry of LMC cluster Cepheids
- Short Name:
- J/A+A/462/599
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work presents IR photometry for two young clusters known to contain sizeable Cepheid populations: NGC 1866 and NGC 2031. The goal is to determine light curves and period-luminosity (PL) relations in the near-IR, to assess the similarity between cluster and field pulsators, and to examine the predictive capability of current pulsation models. The light curves are obtained from multiwavelength broadband J,H,Ks photometry of Cepheids in both clusters, with periods previously established from optical photometry. Mean magnitudes for the Cepheids are used to construct period-luminosity (PL) relations in the near-IR. The properties in the PL planes are compared with the behavior of field Cepheids in the LMC and with the predictions of recent pulsational models, both canonical and overluminous. Cluster and field Cepheids are homogeneous and the inclusion of the cluster Cepheids in the field sample extends the PL relation. The slope of the PL relation is constant over the whole period range and does not show, at least in the adopted IR bands, the break in slope at P~10d reported by some authors. A comparison with the predictions of pulsation models allows an estimate for the distance moduli of NGC 1866 and NGC 2031. The two clusters are found to lie at essentially the same distance. Fitting of theoretical models to the data gives, for the K filter, (m-M)_0_=18.62+/-0.10 if canonical models are used and (m-M)_0_=18.42+/-0.10 if overluminous models are used.
- ID:
- ivo://CDS.VizieR/J/AJ/132/2653
- Title:
- JHKs photometry of N11 young stellar objects
- Short Name:
- J/AJ/132/2653
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared observations have been carried out to survey young stellar objects in the second-largest HII region in the Large Magellanic Cloud, N11. A total area of about 700 arcmin2 is covered in the J, H, and Ks bands. We selected a total of 559 OB and 127 Herbig Ae/Be star candidates out of the detected sources based on their near-infrared colors and magnitudes. The existence of these young stellar objects indicates that star formation activity is underway in the whole N11 region. Many Herbig Ae/Be star candidates are distributed around the periphery of the OB association LH 9. Spatial correlations of the OB and Herbig Ae/Be star candidates with the objects observed at other wavelengths (optical, radio continuum, H{alpha}, CO, and X-ray) suggest that the birth of the young stellar populations in peripheral molecular clouds was triggered originally by LH 9. It is likely that the trigger for this star formation was an expanding supershell blown by the OB association. In N11 a new generation of stars would have been formed in the clouds developed from swept-up interstellar medium.
- ID:
- ivo://CDS.VizieR/J/A+A/453/517
- Title:
- JKs photometry of N159A
- Short Name:
- J/A+A/453/517
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared imaging and spectroscopic observations of the HII region N159A (~10pc) in the giant star-forming region N159 (50pc) in the LMC. N159A was observed in the J and Ks bands at high spatial resolution ~0.2" using the ESO Very Large Telescope UT4 (VLT), equipped with the NAOS adaptative optics system. Our data reveal the morphology of this region in unprecedented detail. The protostar P2, one of the first YSOs of Class I identified in the LMC is now resolved in two YSO candidates. The ultracompact HII region LI-LMC 1501W is found to be a tight cluster embedded in a compact HII region ionised by a late O source. A new multiple system composed of a tight star cluster and an YSO candidate, all embedded in compact nebular region (0.4pc) is also detected at the north-east edge of N159A. The stellar population of the whole N159A region appears composed of two main stellar populations, one with an age <3Myr and the other one with a large range of age (300Myr-10Gyr). Using spectroscopy, one of the two exciting O stars in the HII region N159A is classified O5-O6.
- ID:
- ivo://CDS.VizieR/J/MNRAS/341/534
- Title:
- J-type carbon stars in LMC
- Short Name:
- J/MNRAS/341/534
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 1497 carbon stars in the Large Magellanic Cloud (LMC) has been observed in the red part of the spectrum with the 2dF facility on the Anglo-Australian Telescope. Of these, 156 have been identified as J-type (i.e. ^13^C-rich) carbon stars using a technique which provides a clear distinction between J stars and the normal N-type carbon stars that comprise the bulk of the sample, and yields few borderline cases. A simple two-dimensional classification of the spectra, based on their spectral slopes in different wavelength regions, has been constructed and found to be related to the more conventional c and j indices, modified to suit the spectral regions observed. Most of the J stars form a photometric sequence in the K-(J-K) colour-magnitude diagram, parallel to and 0.6mag fainter than the N-star sequence. A subset of the J stars (about 13 per cent) are brighter than this J-star sequence; most of these are spectroscopically different from the other J stars. The bright J stars have stronger CN bands than the other J stars and are found strongly concentrated in the central regions of the LMC. Most of the rather few stars in common with Hartwick and Cowley's sample (1988ApJ...334..135H) of suspected CH stars are J stars. Overall, the proportion of carbon stars identified as J stars is somewhat lower than has been found in the Galaxy. The Na D lines are weaker in the LMC J stars than in either the Galactic J stars or the LMC N stars, and do not seem to depend on temperature.
- ID:
- ivo://CDS.VizieR/J/A+A/510/A19
- Title:
- K-band spectra of 6 LMC globular clusters
- Short Name:
- J/A+A/510/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Current stellar population models have arguably the largest uncertainties in the near-IR wavelength range, partly due to a lack of large and well calibrated empirical spectral libraries. In this paper we present a project whose aim it is to provide the first library of luminosity weighted integrated near-IR spectra of globular clusters to be used to test the current stellar population models and serve as calibrators for future ones. Our pilot study presents spatially integrated K-band spectra of three old (>=10Gyr) and metal poor ([Fe/H]~-1.4), and three intermediate age (1-2Gyr) and more metal rich ([Fe/H]~-0.4) globular clusters in the LMC.
- ID:
- ivo://CDS.VizieR/J/A+AS/122/507
- Title:
- Kinematics of SMC carbon stars
- Short Name:
- J/A+AS/122/507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a radial velocity survey of a sample of the field population of carbon stars in the outer parts of the Small Magellanic Cloud (SMC). This first set of results includes radial velocities for 71 carbon stars, with an individual precision of +/-2-5km/s. The mean heliocentric velocity of the stars (excluding one very high velocity star) is 149.3+/-3.0km/s with a velocity dispersion of 25.2+/-2.1km/s. These values drop to 145.5+/-2.7km/s and 20.6+/-1.9km/s respectively, if we exclude the stars belonging to the Outer Wing. The velocity distribution does not show the multiple peaks seen in some samples of Population I objects. The mass of the SMC as inferred from the above velocity dispersion (without the outer Wing stars) is =~1.2x10^9^M_{sun}_.
