PI: Alexis Finoguenov
Observations: ALFOSC imaging+spectroscopy, NOTCAM imaging

Students: Petteri Nikula, Olli-Pekka Ojala, Harri Tavaila, Elnax Safi

Abstract: We have conducted the survey for galaxy clusters using RASS and SDSS data. In order to infer the exact parameters of the clusters, the knowledge of spectroscopic redshift is essential and we will measure the redshift of 3-5 brightest galaxies of cluster visible during the NOT school. We have obtained deep photometric ugriz data for 31 of the massive cluster at a redshift of 0.5 using CHFT. We will pursue a deep k-band photometry to improve on the photometric redshift estimates for the background galaxies and on the stellar masses for the cluster member galaxies. Above a redshift of 0.5 deeper z-band observations are needed.

Scientific justification: Detailed studies of galaxy clusters in the era of precision cosmology require the best possible knowledge about the clusters. To this end we have been conducting the gravitational lensing study of a sample of well-defined massive clusters, for which we have secured ugriz observation on the CFHT (3.6 meter telescope). In order to best characterized the background galaxy population, addition of NIR filters is a key importance. K-band is the most efficient way to do so, provided that deep z-band observations have been already achieved. Cluster redshift is both required for the precise computation of cluster properties and for the analysis of large-scale structure signal using the correlation function or a power spectrum.

Finding galaxy clusters is a hot topic in the observational cosmology. Large area surveys offer unique prospects for such studies due to their large areas. High-z part of these sample deliver the very rare examples of massive clusters. We have conducted such a study using a combination of ROSAT All-Sky Survey data pushed to unprecedented depths and SDSS photometry, which allowed us to identify the cluster candidates. In order to select the massive clusters, we employ an optical richness, which requires sampling of a 21.5 z-band magnitude at high redshifts. SDSS imaging is too shallow for that. Thus, while the candidate clusters are found, their characterization still needs to be done.

In this project the students will learn how to perform the NOTCam imaging observations, how to reduce the NIR data and extract the photometry. For the provided member galaxies, they can estimate the luminosity function of cluster galaxies in K-band. The students will also learn how to perform the ALFOSC imaging and long-slit observations, how to reduce optical imaging and spectroscopic data, extract the photometry, and how to obtain the redshift of the object. Using the r magnitudes from SDSS and adding the measurements of the z-band, they need to find the cluster members using the red sequence technique. They can also learn to calculate the cluster richness by counting the galaxies down to L*+1.

PI: Heidi Korhonen
Observations: FIES spectroscopy, ALFOSC imaging+spectroscopy

Students: Johanna Lamppu, Shabnam Nikbakhsh, Konsta Lankinen, Joonas Viuho

Abstract: Flares and starspots are the most blatant manifestations of magnetic activity on late-type (FGKM) stars. They are powered by the dynamo-created magnetic fields in the stellar outer convective zone. This activity is supposedly non-existent in hotter stars of earlier spectral types, which have radiative outer envelopes. Recent Kepler satellite observations have revealed flares in ~1.5% of A-type stars. With FIES and ALFOSC observations we will probe some possible explanations for these theoretically unexplained results.

Scientific justification: Our Sun is known to harbour magnetic fields which cause myriad of phenomena, e.g., flares and starspots. It is widely accepted that the global behaviour of the solar magnetic field can be explained by a dynamo action which is due to interaction between magnetic fields and fluid motions. The Sun is thought to have an alphaOmega-type dynamo, in which the poloidal field is created from the toroidal one by helical turbulence (alpha-effect), and the toroidal field is obtained by shearing the already existing poloidal field by differential rotation (Omega-effect). The alphaOmega-dynamo is also thought to work in other main-sequence stars with similar internal structure as the Sun has.

When the stars become more massive and hotter, the outer convective envelope becomes more shallow. A-type stars are thought to not have significant subsurface convection and thus cannot generate a magnetic field via the dynamo operation. This, in turn, means that A-type stars are not expected to flare or have temperature spots. Recent analysis of Kepler data shows that, contrary to the expectations, 1.5% of A-type stars do flare and some also show light-curve variations that are reminiscent of the starspot caused changes seen in the late-type stars (Balona 2012, MNRAS, 423, 3420; Balona 2013, MNRAS, 431, 2240).

These results imply serious problems in our understanding of creation of stellar magnetic fields. However, there are two possible explanations for these results which do not require revision of dynamo theory: 1) flaring A-star have a late-type companion, or 2) the spectral classification of these stars, which is based on the notoriously inaccurate Kepler input catalogue, is wrong.

To clarify these two points we will obtain FIES and ALFOSC spectra of the brightest flaring A-stars in the Kepler field. The FIES spectra of six brightest flaring A-type stars obtained at two different epochs will be used for studying possible radial velocity variations caused by possible binarity, and accurate spectral types will be obtained from the ALFOSC spectra and photometry for approximately 20 flaring A-type stars. If we can rule out both of these possible explanations for the flaring, the implications to our understanding of stellar magnetism are ground-breaking.

PI: Andrew Mason
Observations: ALFOSC spectroscopy + NOTCam imaging

Students: Homa Ghasemi, Ari Takalo, Carlton Xavier, Yaroslav Litus

Abstract: The identification of several new categories of High Mass X-ray Binaries (HMXBs) by the INTEGRAL Gamma-ray observatory in the last decade has prompted strenuous efforts, both observationally and theoretically, to understand the nature of these rare types of X-ray binary system. This programme will assist these efforts by identifying the optical counterparts within a number of systems. This will significantly increase the number of known systems, potentially shedding new light on the prevailing accretion mechanisms, whilst also increasing the statistics of the known population.

Scientific justification: INTEGRAL began observations in 2002 and since then has discovered many new hard X-ray sources including Low-Mass X-ray Binaries (LMXBs), Cataclysmic Variables (CVs) and HMXBs. However, the nature of ~ one third of IGR sources has not been identified (http://irfu.cea.fr/Sap/IGR-Sources/). Important INTEGRAL discoveries are two new classes of HMXB. These are systems with a high level of intrinsic absorption, sgB[e] stars (e.g. IGR J16318-4848 - Chaty, S. et al, 2008, A&A, 484, 783) also Supergiant Fast X- ray Transients (SFXTs) (e.g. IGR J17544-2619 (Sidoli et al, 2009, MNRAS, 397, 1528)). These populations of HMXB systems are short-lived and rare, but their study is important, as they are likely progenitors of extremely compact binary objects, and provide insights into the evolution of high-energy binary systems.

INTEGRAL has been so successful in finding new hard X-ray sources due to its wide field-of-view. However, the localisation accuracy of detected sources is low with a positional uncertainty of a few arcmins. This accuracy is not sufficient to identify the correct optical counterpart. Without an understanding of the source across multiple wavelength ranges, it is difficult to understand the physical nature of the X-ray emission/type of system. To identify an optical counterpart arcsecond positional accuracy is required. We will observe two INTEGRAL sources IGR J19284+0107 and IGR J19475+0049 using optical spectroscopy to identify and spectrally classify the optical counterparts to these systems. These two sources have previously been observed with XMM-Newton and ROSAT, constraining the uncertainties on their positions to 4“ and 14” respectively. The identification of any of the candidate counterparts as an OB star would confirm these systems as HMXBs.

We will also conduct Near Infrared (NIR) photometry of these two sources in addition to 3 other INTEGRAL sources. We will employ J,H,K and Br-gamma filters to construct a Colour Magnitude Diagram (CMD) of the field surrounding each source. This CMD will enable us to separate and identify any High Mass stars from the field population. The Brackett gamma filter will identify any strong sources of Brackett gamma emission, which is a key accretion indicator in the NIR. The identification of any of these systems as SFXTs will be important, as the current number of system is small (~10) and increasing the population will potentially allow us to determine the orbital period and hence accretion mechanism in these mysterious systems.

Splat-VO

PI: Seppo Mattila
Observations: ALFOSC imaging+spectroscopy, NOTCam imagin

Students: Joonatan Ala-Könni, Teemu Willamo, Akke Viitanen, Suvi Korhonen

Abstract: This project will make use of optical long-slit spectroscopy and optical + near-infrared photometry of newly discovered supernovae with the NOT. The spectroscopic observations will be used to investigate the SN types, the epochs after the explosion, expansion velocities, and the SN host galaxy redshifts. The SN absolute magnitudes and colours will be compared with data for well-observed SNe of similar types from the literature to complement the spectroscopy and to search for evidence of an IR excess due to dust local to the SN.

Scientific Justification: Massive stars (initially above ~8 solar masses) end their lives in core-collapse supernova (CCSN) explosions which are among the most violent events in the universe. During the last decade the interest on CCSNe has increased substantially. Their observed connection with gamma­ray bursts (GRBs; for review see Woosley & Bloom 2006, ARA&A, 44, 507) and the direct detections of their progenitor stars (for review see Smartt 2009, ARA&A, 47, 63) in pre-explosion images are examples of the recent breakthroughs made on this field. The role of CCSNe as the main source of interstellar dust seen in the early Universe has also recently been actively discussed and debated (e.g., Dwek et al. 2007, ApJ, 662, 9 27).

In a half night of observations the students will be able to observe ~5-7 SNe. Some supernova candidates with a spectroscopic confirmation still missing will also be included in the observations. Spectroscopic observations will be used to determine the types of the observed SNe by identifying characteristic spectral lines and by cross correlating (e.g., using the GELATO tool, https://gelato.tng.iac.es/) with libraries of SN spectra. Some SN candidates with a spectroscopic confirmation still missing can be reported in a Central Bureau Electronic Telegram (http://www.cbat.eps.harvard.edu/) immediatelly after the night of observations. The spectral line profiles will be investigated and the dominant line broadening mechanism identified and discussed. The host galaxy redshifts will be determined to obtain SN distances required to determine the absolute magnitudes and luminosities.

Optical and near-IR imaging will be obtained in the broad band (UBVRIJHKs) filters to determine the SN absolute magnitude and colours. These will be compared with well observed SNe of the same type from the literature and by combination with the photometry often available in the web (e.g. from amateurs, see http://www.rochesterastronomy.org/snimages/) SN light curves will be plotted and investigated. The near-IR observations will be particularly interesting for searching for evidence of an infrared-excess caused by the reprocessing of energy by dust local to the SN. Such dust can be pre-existing in the circumstellar medium of the progenitor star or newly formed in the SN ejecta.

Near-IR imaging of a couple of well-observed nearby luminous infrared galaxies with extremely high SFRs and therefore also very high SN rates (~1 SN/yr) will also be obtained to search for a newly exploded SN by comparison to previous reference images.

PI: Kari Nilsson
Observations: ALFOSC imaging and spectroscopy + NOTCam imaging

Students: Joonas Saario, Toni Tuominen, Jussi Harmanen, Marzieh Khansari

Abstract: This project aims to obtain UBVRIJHK imaging and optical spectroscopy of the Crab Nebula in order to study a) The broadband spectral energy distribution (SED) of the Crab pulsar and the dynamic features (“knot”,“anvil” and the “wisps”) in its vicinity and b) to estimate the contamination of the synchrotron continuum emission by the emission lines. The project will familiarize the students with basic imaging and spectroscopic techniques and illustrate the relationship between spectral and spatial information.

Scientific justification: The immediate vicinity of the Crab Nebula pulsar is highly active due to an ultrarelativistic wind blowing from the neutron star. When the wind hits the termination shock, highly variable synchrotron emission is created. In addition, synchrotron emission from the pulsar jet and line emission from the filaments is observed from the Crab. Among the most dynamic features are the “knot” (0.6“ from the pulsar), possibly a shock feature close to the pulsar, the “wisps” (7-10 arcsec), shock features further away from the pulsar and the “anvil” (4 arcsec), the turbulent base of the jet. These synchrotron features change noticeably (from the ground) within a few weeks.

This project aim to obtain UBVRIJHK imaging of the nebula and longslit spectroscopy at 3 locations (on the pulsar and two adjacent positions) with ALFOSC. The aims are:

1) To study the SED of the pulsar and the active regions mentioned above and compare them to the literature values. For some regions this is the first time such a broad spectrum is constructed. Possible breaks in the spectrum may give clues to the acceleration mechanism. The images can also be used for the ongoing Crab monitoring project at the NOT. Comparing the I-band image to I-band image taken in 2010-2012 by the monitoring project the variability of the nebula can be studied.

2) To study how much the broadband fluxes are affected by line emission contamination. Three longslit spectra will be obtained to study the dependence on location and line fluxes derived. The strongest lines are 5007 [OIII], 6563 H_alpha+[NII] and 6717[SII].

The project will introduce the students into basic observation & reduction techniques of optical & NIR imaging + optical spectroscopy. The images will contain clearly visible line emission features in some bands, which in conjunction with the longslit spectra clearly illustrate the relationship between imaging and the spatial information in the spectra. ALFOSC imaging data in a few optical bands is available as backup. By the start of the course, NIR data may also become available for this purpose.