Infrared spectroscopy of eruptive variable protostars from VVV

In a companion work (Paper I), we detected a large population of highly variable Young Stellar Objects (YSOs) in the Vista Variables in the Via Lactea (VVV) survey, typically with class I or flat spectrum spectral energy distributions and diverse light-curve types. Here we present infrared spectra (0.9–2.5??m) of 37 of these variables, many of them observed in a bright state. The spectra confirm that 15/18 sources with eruptive light curves have signatures of a high accretion rate, either showing EXor-like emission features (?v = 2 CO, Br?) and/or FUor-like features (?v = 2 CO and H2O strongly in absorption). Similar features were seen in some long-term periodic YSOs and faders but not in dippers or short-term variables. The sample includes some dusty Mira variables (typically distinguished by smooth Mira-like light curves), two cataclysmic variables and a carbon star. In total, we have added 19 new objects to the broad class of eruptive variable YSOs with episodic accretion. Eruptive variable YSOs in our sample that were observed at bright states show higher accretion luminosities than the rest of the sample. Most of the eruptive variables differ from the established FUor and EXor subclasses, showing intermediate outburst durations and a mixture of their spectroscopic characteristics. This is in line with a small number of other recent discoveries. Since these previously atypical objects are now the majority amongst embedded members of the class, we propose a new classification for them as MNors. This term (pronounced emnor) follows V1647 Ori, the illuminating star of McNeil's Nebula

(Sub)mm Interferometry Applications in Star Formation Research

This contribution gives an overview about various applications of (sub)mm interferometry in star formation research. The topics covered are molecular outflows, accretion disks, fragmentation and chemical properties of low- and high-mass star-forming regions. A short outlook on the capabilities of ALMA is given as well.Comment: 20 pages, 7 figures, in proceedings to "2nd European School on Jets from Young Star: High Angular Resolution Observations". A high-resolution version of the paper can be found at http://www.mpia.de/homes/beuther/papers.htm

Photometric variability of massive young stellar objects

The Vista Variables in the Via Lactea (VVV) survey has allowed for an unprecedented number of multi-epoch observations of the southern Galactic plane. In a recent paper, 13 massive young stellar objects (MYSOs) have already been identified within the highly variable (?Ks > 1 mag) YSO sample of another published work. This study aims to understand the general nature of variability in MYSOs. Here we present the first systematic study of variability in a large sample of candidate MYSOs. We examined the data for variability of the putative driving sources of all known Spitzer extended green objects (EGOs; 270) and bright 24 ?m sources coinciding with the peak of 870 ?m detected ATLASGAL clumps (448), a total of 718 targets. Of these, 190 point sources (139 EGOs and 51 non-EGOs) displayed variability (IQR > 0.05, ?Ks > 0.15 mag). 111 and 79 light-curves were classified as periodic and aperiodic respectively. Light-curves have been sub-classified into eruptive, dipper, fader, short-term-variable and long-period-variable-YSO categories. Lomb-Scargle periodogram analysis of periodic light-curves was carried out. 1–870 ?m spectral energy distributions of all the variable sources were fitted with YSO models to obtain the representative properties of the variable sources. 41% of the variable sources are represented by > 4 M? objects, and only 6% were modelled as > 8 M? objects. The highest-mass objects are mostly non-EGOs, and deeply embedded, as indicated by nearly twice the extinction when compared with EGO sources. By placing them on the HR diagram we show that most of the lower mass, EGO type objects are concentrated on the putative birth-line position, while the luminous non-EGO type objects group around the zero-age-main-sequence track. Some of the most luminous far infrared (FIR) sources in the massive clumps and infrared quiet driving sources of EGOs have been missed out by this study owing to an uniform sample selection method. A high rate of detectable variability in EGO targets (139 out of 153 searched) implies that near-infrared variability in MYSOs is closely linked to the accretion phenomenon and outflow activity

The sharp ALMA view of infall and outflow in the massive protocluster G31.41+0.31

Interstellar matter and star formatio

Dome C observations of massive protostars

The importance of a Dome C facility for studies of massive star formation is highlighted. Using an example of a statistical study of 380 candidate massive protostars based on the GLIMPSE legacy program data from the Spitzer Space Telescope, the relevance of a Dome C facility for further science progress is argued. The GLIMPSE point source photometry was used to a conduct colour-magnitude analysis, and radiative transfer modelling of the spectral energy distributions of the massive protostars. The results support an accretion scenario for the process of massive star formation up to masses of 50 M๏. The available spectral energy distrubutions of the massive protostellar candidates are largely inadequate in the crucial bands from 10–500 μm. This wavelength range can be effectively filled in with a nominal Dome C observing facility which can be highly cost effective compared to a space facility. Narrow-band emission line imaging of massive star forming regions in the 10–20 micron bands using high temperature emission lines can yield invaluable information on the nature of OB stars in the Milky Way and nearby galaxies. Such observations are crucial for our understanding of the influence of OB stars in controlling the galactic turbulence, feedback effects, influence on other low mass stars in the vicinity, and controlling the star formation rate

Changing structures in galactic star clusters

We investigate the structures of embedded and open clusters using statistical methods, in particular the combined parameter \Q, which permits to quantify the cluster structure. Star clusters build up from several subclusters evolving from a structured to a more centrally concentrated stage. The evolution is not only a function of time, but also of the mass of the objects. Massive stars are usually centrally concentrated, while lower-mass stars are more widespread, reflecting the effect of mass segregation. Using this method we find that in IC 348 and the Orion Nebula Cluster the spatial distribution of brown dwarfs does not follow the central clustering of stars, giving important clues to their formation mechanism by supporting the ejected embryo scenario

Generalized Nabla Differentiability and Integrability for Fuzzy Functions on Time Scales

This paper mainly deals with introducing and studying the properties of generalized nabla differentiability for fuzzy functions on time scales via Hukuhara difference. Further, we obtain embedding results on E n for generalized nabla differentiable fuzzy functions. Finally, we prove a fundamental theorem of a nabla integral calculus for fuzzy functions on time scales under generalized nabla differentiability. The obtained results are illustrated with suitable examples

STATCOM prototype in voltage control mode to assess its behavior in electric power networks

We present the results of a morphological study performed to a sample of Ultracompact (UC) H II regions with Extended Emission (EE) using Spitzer-IRAC imagery and 3.6 cm VLA conf. D radio-continuum (RC) maps. Some examples of the comparison between maps and images are presented. Usually there is an IR point source counterpart to the peak(s) of RC emission, at the position of the UC H II source. We find that the predominant EE morphology is the cometary, and in most cases is coincident with IR emission at 8.0 ?m. Preliminary results of Spitzer-IRAC photometry of a sub-sample of 13 UC H II regions with EE (UC H II + EE) based on GLIMPSE legacy data are also presented. Besides, individual IRAC photometry was performed to 19 UC H II sources within these 13 regions. We show that UC H II sources lie on specific locus, both in IRAC color-color and AM-product diagnostic diagrams. Counts of young stellar sources are presented for each region, and we conclude that a proportion of ?2%, ?10%, and ?88% of sources in UC H II + EEare, in average, Class I, II, and III, respectively. " 2010: Instituto de Astronomía, UNAM.",,,,,,,,,"http://hdl.handle.net/20.500.12104/44691","http://www.scopus.com/inward/record.url?eid=2-s2.0-80055017449&partnerID=40&md5=c8e856b161131910ba39454e6c12ffc8",,,,,,,,"Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias",,"1

Spitzer-IRAC imagery and photometry of Ultracompact H II regions with Extended Emission

We present the results of a morphological study performed to a sample of Ultracompact (UC) H II regions with Extended Emission (EE) using Spitzer-IRAC imagery and 3.6 cm VLA conf. D radio-continuum (RC) maps. Some examples of the comparison between maps and images are presented. Usually there is an IR point source counterpart to the peak(s) of RC emission, at the position of the UC H II source. We find that the predominant EE morphology is the cometary, and in most cases is coincident with IR emission at 8.0 μm. Preliminary results of Spitzer-IRAC photometry of a sub-sample of 13 UC H II regions with EE (UC H II + EE) based on GLIMPSE legacy data are also presented. Besides, individual IRAC photometry was performed to 19 UC H II sources within these 13 regions. We show that UC H II sources lie on specific locus, both in IRAC color-color and AM-product diagnostic diagrams. Counts of young stellar sources are presented for each region, and we conclude that a proportion of ∼2%, ∼10%, and ∼88% of sources in UC H II + EEare, in average, Class I, II, and III, respectively. © 2010: Instituto de Astronomía, UNAM